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Monitor Calibration Update

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Monitor Calibration Update

Okay, so I no longer NEED a new monitor, because I’ve got one – and my wallet is in Leighton Hospital Intensive Care Unit on the critical list..

What have you gone for Andy?  Well if you remember, in my last post I was undecided between 24″ and 27″, Eizo or BenQ.  But I was favoring the Eizo CS2420, on the grounds of cost, both in terms of monitor and calibration tool options.

But I got offered a sweet deal on a factory-fresh Eizo CS270 by John Willis at Calumet – so I got my desire for more screen real-estate fulfilled, while keeping the costs down by not having to buy a new calibrator.

monitor calibration update

But it still hurt to pay for it!

Monitor Calibration

There are a few things to consider when it comes to monitor calibration, and they are mainly due to the physical attributes of the monitor itself.

In my previous post I did mention one of them – the most important one – the back light type.

CCFL and WCCFL – cold cathode fluorescent lamps, or LED.

CCFL & WCCFL (wide CCFL) used to be the common type of back light, but they are now less common, being replaced by LED for added colour reproduction, improved signal response time and reduced power consumption.  Wide CCFL gave a noticeably greater colour reproduction range and slightly warmer colour temperature than CCFL – and my old monitor was fitted with WCCFL back lighting, hence I used to be able to do my monitor calibration to near 98% of AdobeRGB.

CCFL back lights have one major property – that of being ‘cool’ in colour, and LEDs commonly exhibit a slightly ‘warmer’ colour temperature.

But there’s LEDs – and there’s LEDs, and some are cooler than others, some are of fixed output and others are of a variable output.

The colour temperature of the backlighting gives the monitor a ‘native white point’.

The ‘brightness’ of the backlight is really the only true variable on a standard type of LCD display, and the inter-relationship between backlight brightness and colour temperature, and the size of the monitors CLUT (colour look-up table) can have a massive effect on the total number of colours that the monitor can display.

Industry-standard documentation by folk a lot cleverer than me has for years recommended the same calibration target settings as I have alluded to in previous blog posts:

White Point: D65 or 6500K

Brightness: 120 cdm² or candelas per square meter

Gamma: 2.2

monitor calibration update

The ubiquitous ColorMunki Photo ‘standard monitor calibration’ method setup screen.

This setup for ‘standard monitor calibration’ works extremely well, and has stood me in good stead for more years than I care to add up.

As I mentioned in my previous post, standard monitor calibration refers to a standard method of calibration, which can be thought of as ‘software calibration’, and I have done many print workshops where I have used this method to calibrate Eizo ColorEdge and NEC Spectraviews with great effect.

However, these more specialised colour management monitors have the added bonus of giving you a ‘hardware monitor calbration’ option.

To carry out a hardware monitor calibration on my new CS270 ColorEdge – or indeed any ColorEdge – we need to employ the Eizo ColorNavigator.

The start screen for ColorNavigator shows us some interesting items:

monitor calibration update

The recommended brightness value is 100 cdm² – not 120.

The recommended white point is D55 not D65.

Thank God the gamma value is the same!

Once the monitor calibration profile has been done we get a result screen of the physical profile:

monitor calibration update

Now before anyone gets their knickers in a knot over the brightness value discrepancy there’s a couple of things to bare in mind:

  1. This value is always slightly arbitrary and very much dependent on working/viewing conditions.  The working environment should be somewhere between 32 and 64 lux or cdm² ambient – think Bat Cave!  The ratio of ambient to monitor output should always remain at between 32:75/80 and 64:120/140 (ish) – in other words between 1:2 and 1:3 – see earlier post here.
  2. The difference between 100 and 120 cdm² is less than 1/4 stop in camera Ev terms – so not a lot.

What struck me as odd though was the white point setting of D55 or 5500K – that’s 1000K warmer than I’m used to. (yes- warmer – don’t let that temp slider in Lightroom cloud your thinking!).

monitor calibration updateAfter all, 1000k is a noticeable variation – unlike the brightness 20cdm² shift.

Here’s the funny thing though; if I ‘software calibrate’ the CS270 using the ColorMunki software with the spectro plugged into the Mac instead of the monitor, I visually get the same result using D65/120cdm² as I do ‘hardware calibrating’ at D55 and 100cdm².

The same that is, until I look at the colour spaces of the two generated ICC profiles:

monitor calibration update

The coloured section is the ‘software calibration’ colour space, and the wire frame the ‘hardware calibrated’ Eizo custom space – click the image to view larger in a separate window.

The hardware calibration profile is somewhat larger and has a slightly better black point performance – this will allow the viewer to SEE just that little bit more tonality in the deepest of shadows, and those perennially awkward colours that sit in the Blue, Cyan, Green region.

It’s therefore quite obvious that monitor calibration via the hardware/ColorNavigator method on Eizo monitors does buy you that extra bit of visual acuity, so if you own an Eizo ColorEdge then it is the way to go for sure.

Having said that, the differences are small-ish so it’s not really worth getting terrifically evangelical over it.

But if you have the monitor then you should have the calibrator, and if said calibrator is ‘on the list’ of those supported by ColorNavigator then it’s a bit of a JDI – just do it.

You can find the list of supported calibrators here.

Eizo and their ColorNavigator are basically making a very effective ‘mash up’ of the two ISO standards 3664 and 12646 which call for D65 and D50 white points respectively.

Why did I go CHEAP ?

Well, cheaper…..

Apart from the fact that I don’t like spending money – the stuff is so bloody hard to come by – I didn’t want the top end Eizo in either 27″ or 24″.

With the ‘top end’ ColorEdge monitors you are paying for some things that I at least, have little or no use for:

  • 3D CLUT – I’m a general sort of image maker who gets a bit ‘creative’ with my processing and printing.  If I was into graphics and accurate repro of Pantone and the like, or I specialised in archival work for the V & A say, then super-accurate colour reproduction would be critical.  The advantage of the 3D CLUT is that it allows a greater variety of SUBTLY different tones and hues to be SEEN and therefore it’s easier to VISUALLY check that they are maintained when shifting an image from one colour space to another – eg softproofing for print.  I’m a wildlife and landscape photographer – I don’t NEED that facility because I don’t work in a world that requires a stringent 100% colour accuracy.
  • Built-in Calibrator – I don’t need one ‘cos I’ve already got one!
  • Built-in Self-Correction Sensor – I don’t need one of those either!

So if your photography work is like mine, then it’s worth hunting out a ‘zero hours’ CS270 if you fancy the extra screen real-estate, and you want to spend less than if buying its replacement – the CS2730.  You won’t notice the extra 5 milliseconds slower response time, and the new CS2730 eats more power – but you do get a built-in carrying handle!

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Your Monitor – All You Ever Wanted to Know

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Your Monitor – All You Ever Wanted to Know, and the stuff you didn’t – but need to!

I need a new monitor, but am undecided which to buy.  I know exactly which one I’d go for if money was no object – the NEC Spectraview Reference 302, but money is a very big object in that I ain’t got any spare!

But spend it I’ll have to – your monitor is the window on to your images and so is just about THE most important tool in your photographic workflow.  I do wish people would realize/remember that!

Right now my decision is between 24″ and 27″, Eizo or BenQ.  The monitor that needs replacement due to backlight degradation is my trusty HP LP2475W – a wide gamut monitor that punched way above its original price weight, and if I could find a new one I’d buy it right now – it was THAT good.

Now I know more than most about the ‘numbers bit’ of photography, and this current dilemma made me think about how much potential for money-wasting this situation could be for those that don’t ‘understand the tech’ quite as much as I do.

So I thought I’d try and lay things out for you in a simple and straight forward blog post – so here goes.

The Imaging Display Chain

Image Capture:

Let’s take my landscape camera – the Nikon D800E.  It is a 36 megapixel DSLR set to record UNCOMPRESSED 14 bit Raw files.

The RAW image produced by this camera has a pixel dimension of 7360 x 4912 and a pixel area of 36,152,320 pixels.

The horizontal resolution of this beastly sensor is approximately 5200 pixels per inch, each pixel being 4.88 µm (microns) in diameter – that’s know as pixel pitch.

During the exposure, the ANALOGUE part of the senor sees the scene in full spectrum colour and tone through its Bayer Array – it gathers an analogue image.

When the shutter closes, the DIGITAL side of the imaging sensor then basically converts the analogue image into a digital render with a reproduction accuracy of 14 bits per pixel.

And let’s not forget the other big thing – colour space.  All dslr cameras capture their images in their very own unique sensor colour space.  This bares little to no resemblance to either of the three commonly used digital colour management workflow colour spaces of sRGB, AdobeRGB1998 or ProPhotoRGB.

But for the purposes of digital RAW workflow, RAW editors such as Lightroom do an exceptional job of conserving the majority if not all the colours captured by the camera sensor, by converting the capture colour space to that of ProPhotoRGB – basically because it’s by far the largest industry standard space with the greatest spread of HSL values.

So this RAW file that sits on my CF card, then gets ingested by my Mac Pro for later display on my monitor is:

  • 1.41 inches on its long edge
  • has a resolution of around 5,200 pixels per inch
  • has a reproduction accuracy for Hue, Saturation & Luminance of 14 bits
  • has a colour space unique to the camera, which can best be reproduced by the ProPhotoRGB working colour space.

Image Display:

Now comes the tricky bit!

In order to display an image on a monitor, said monitor has to be connected to your computer via your graphics card or GPU output. This creates a larger number of pitfalls and bear traps for the unsuspecting and naive!

Physical attributes of a monitor you need to bare in mind:

  1. Panel Display Colour Bit Depth
  2. Panel Technology – IPS etc
  3. Monitor Panel Backlight – CCFL, WCCFL, LED etc
  4. Monitor Colour Look-Up Table – Monitor On-Board LUT (if applicable)
  5. Monitor connectivity
  6. Reliance on dedicated calibration device or not

The other consideration is your graphics card Colour Look-Up Table – GPU LUT

1.Monitor Panel Display Colour Bit Depth – All display monitors have a panel display colour bit depth – 8 bit or 10 bit.

I had a client turn up here last year with his standard processing setup – an oldish Acer laptop and an Eizo Colour Edge monitor – he was very proud of this setup, and equally gutted at his stupidity when it was pointed out to him.

The Eizo was connected to the laptop via a DVI to VGA lead, so he had paid a lot of good money for a 10 bit display monitor which he was feeding via a connection that was barely 8 bit.

Sat next to the DVI input on the Eizo was a Display Port input – which is native 10 bit. A Display Port lead doesn’t cost very much at all and is therefore the ONLY sensible way to connect to a 10 bit display – provided of course that your machine HAS a Display Port output – which his Acer laptop did not!

So if you are looking at buying a new monitor make sure you buy one with a display bit depth that your computer is capable of supporting.

There is visually little difference between 10 bit and 8 bit displays until you view an image at 100% magnification or above – then you will usually see something of an increase in colour variation and tonal shading, provided that the image you are viewing has a bit depth of 10+.  The difference is often quoted at its theoretical value of 64x –  (1,073,741,824 divided by 16,777,216).

So, yes, your RAW files will LOOK and APPEAR slightly better on a 10 bit monitor – but WAIT!

There’s more….how does the monitor display panel achieve its 10 bit display depth?  Is it REAL or is it pseudo? Enter FRC or Frame rate Control.

The FRC spoof 10 bit display – frame rate control quite literally ‘flickers’ individual pixels between two different HSL values at a rate fast enough to be undetectable by the human eye – the viewers brain gets fooled into seeing an HSL value that isn’t really there!

monitor

Here’s why I hate FRC !

Personally I have zero time for FRC technology in panels – I’d much prefer a good solid 8 bit wide gamut panel without it than a pseudo 10 bit; which is pretty much the same 8 bit panel with FRC tech and a higher price tag…Caveat Emptor!

2. Panel Technology – for photography there is only really one tech to use, that of IPS or In Plane Switching.  The main reasons for this are viewing angle and full colour gamut.

The more common monitors, and cheaper ones most often use TN tech – Twisted Nematic, and from a view angle point of view these are bloody awful because the display colour and contrast vary hugely with even just an inch or two head movement.

Gamers don’t like IPS panels because the response time is slow in comparison to TN – so don’t buy a gaming monitor for your photo work!

There are also Vertical Alignment (VA) and Plane to line Switching (PLS) technologies out there, VA being perhaps marginally better than TN, and PLS being close to (and in certain cases better than) IPS.

But all major colour work monitor manufacturers use IPS derivative tech.

3. Monitor Panel Backlight – CCFL, WCCFL, LED

All types of TFT (thin film transistor) monitor require a back light in order to view what is on the display.

Personally I like – or liked before it started to get knackered – the wide cold cathode fluorescent (WCCFL) backlight on the HP LP2475W, but these seem to have fallen by the wayside somewhat in favour of LED backlights.

The WCCFL backlight enabled me to wring 99% of the Adobe1998 RGB colourspace out of a plain 8 bit panel on the old HP, and it was a very even light across the whole of the monitor surface.  The monitor itself is nearly 11 years old, but it wasn’t until just over 12 months ago that it started to fade at the corners.  Only since the start of this year (2017) has it really begun to show signs of more severe failure on the right hand 20% – hence I’ll be needing a new one soonish!

But modern LED backlights have a greater degree of uniformity – hence their general supersedence of WCCFL.

4. Colour Look-Up Tables or LUTs

Now this is a bit of an awkward one for some folk to get their heads around, but really it’s simple.

Most monitors that you can buy have an 8 bit LUT which is either fixed, or variable via a number of presets available within the monitor OSD menu.

When it comes to calibrating a ‘standard gamut with fixed LUT’ monitor, the calibration software makes its alterations to the LUT of the GPU – not that of the monitor.

With monitors and GPUs that are barely 8 bit to begin with, the act of calibration can lead to problems.

A typical example would be an older laptop screen.  A laptop screen is driven by the on-board graphics component or chipset within the laptop motherboard.  Older MacBooks were the epitome of this setups failure for photographers.

The on-board graphics in older MacBooks were barely 8 bit from the Apple factory, and when you calibrated them they fell to something like 6 bit, and so a lot of images that contained varied tones of a similar Hue displayed colour banding:

monitor

An example of image colour banding due to low GPU LUT bit depth.
The banding is NOT really there, it just illustrates the lack of available colours and tones for the monitor display.

This phenomenon used to be a pain in the bum when choosing images for a presentation, but was never anything to panic over because the banding is NOT in the image itself.

Now if I display this same RAW file in Lightroom on my newer calibrated 15″ Retina MacBook Pro I still see a tiny bit of banding, though it’s not nearly this bad.  However, if I connect an Eizo CS2420 using a DisplayPort to HDMI cable via the 10 bit HDMI port on the MBP then there is no banding at all.

And here’s where folk get confused – none of what we are talking about has a direct effect on your image – just on how it appears on the monitor.

When I record a particular shade of say green on my D800E the camera records that green in its own colour space with an accuracy of 14 bits per colour channel.  Lightroom will display it’s own interpretation of that colour green.  I will make adjustments to that green in HSL terms and then ask Lightroom to export the result as say a TIFF file with 16 bits of colour accuracy per channel – and all the time this is going on I’m viewing the process on a monitor which has a display colour bit depth of 8 bit or 10 bit and that is deriving its colour from a LUT which could be 8 bit, 14 bit or 16 bit depending on what make and model monitor I’m using!

Some people get into a state of major confusion when it comes to bits and bit depth, and to be honest there’s no need for it.  All we are talking about here is ‘fidelity of reproduction’ on the monitor of colours which are FIXED and UNALTERABLE in your RAW file, and of the visual impact of your processing adjustments.

The colours contained in our image are just numbers – nothing more than that.

Lightroom will display an image by sending colour numbers through the GPU LUT to the monitor.  I can guarantee you that even with the best monitor in the world in conjunction with the most accurate calibration hardware money can buy, SOME of those colour numbers will NOT display correctly!  They will be replaced in a ‘relative colourmetric manner’ by their nearest neighbor in the MONITOR LUT – the colours the monitor CAN display.

Expensive monitors with 14 bit or 16 bit LUTs mean less colours will be ‘replaced’ than when using a monitor that has an 8 bit LUT, and even more colours will be replaced if we scale back our ‘spend’ even further and purchase a standard gamut sRGB monitor.

Another advantage of the pricier 14/16 bit wide gamut dedicated photography monitors from the likes of Eizo, NEC and BenQ is the ability to do ‘hardware calibration’.

Whereas the ‘standard’ monitor calibration mentioned earlier makes it’s calibration changes primarily to the GPU LUT, and therefore somewhat ‘stiffles’ its output bit depth; with hardware calibration we can internally calibrate the monitor itself and leave the GPU running as intended.

That’s a slight over-simplification, but it makes the point!

5. Monitor Connectivity. By this I mean connection type:

monitor

VGA or D-Sub 15. Awful method of connection – went out with the Ark. If you are using this then “stop it”!

monitor

DVI – nothing wrong with this connection format whatsoever, but bare in mind it’s an 8 bit connection.

monitor

Dual Link DVI – still only 8 bit.

monitor

Displayport – 10 bit monitor input connection.

monitor

HDMI left, Displayport right – both 10 bit connections.

6. Reliance on dedicated calibration device or not – this is something that has me at the thin end of a sharp wedge if I consider the BenQ option.

I own a perfectly serviceable ColorMunki Photo, and as far as I can see, hardware calibration on the Eizo is feasible with this device. However, hardware calibration on BenQ system software does not appear to support the use of my ColorMunki Photo – so I need to purchase an i1 Display, which is not a corner I really want to be backed into!

Now remember how we defined my D800E Raw file earlier on:

  • has a pixel dimension of 7360 x 4912 and a pixel area (or resolution) of 36,152,320 pixels.
  • 1.41 inches on its long edge
  • has a resolution of around 5,200 pixels per inch
  • has a reproduction accuracy for Hue, Saturation & Luminance of 14 bits
  • has a colour space unique to the camera, which can best be reproduced by the ProPhotoRGB working colour space.

So let’s now take a look at the resolution spec for, say, the NEC Spectraview Reference 302 monitor.  It’s a 30″ panel with an optimum resolution of 2560 x 1600 pixels – that’s 4Mp!

The ubiquitous Eizo ColorEdge CG2420 has a standard 24 inch resolution of 1920 x 1200 pixels – that’s 2.3Mp!

The BenQ SW2700PT Pro 27in IPS has 2560 x 1440, or 3.68Mp resolution.

Yes, monitor resolution is WAY BELOW that of the image – and that’s a GOOD THING.

I HATE viewing unedited images/processing on my 13″ Retina MBP screen – not just because of any possible calibration issue, or indeed that of its diminutive size – but because of its whopping 2560 x 1600, 4Mp resolution crammed into such a small space.

The individual pixels are so damn tiny the lull you into a false sense of security about one thing above all else – critical image sharpness.

Images that ‘appear tack sharp’ on a high resolution monitor MIGHT prove a slight disappointment when viewed on another monitor with a more conventional resolution!

So there we have it, and I hope you’ve learned something you didn’t know about monitors.

And remember, understanding what you already have, and what you want to buy is a lot more advantageous to you than the advice of some bloke in a shop who’s on a sales commission!

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Monitor Brightness.

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Monitor Brightness & Room Lighting Levels.

I had promised myself I was going to do a video review of my latest purchase – the Lee SW150Mk2 system and Big and Little Stopper filters I’ve just spent a Kings ransom on for my Nikon 14-24mm and D800E:

Lee SW150 mk2,Lee Big Stopper,Lee Little Stopper,Lee Filters, Nikon 14-24, Nikon, Nikon D800E, landscape photography,Andy Astbury,Wildlife in Pixels

PURE SEX – and I’ve bloody well paid for this! My new Lee SW150 MkII filter system for the Nikon 14-24. Just look at those flashy red anodised parts – bound to make me a better photographer!

But I think that’ll have to wait while I address a question that keeps cropping up lately.  What’s the question?

Well, that’s the tricky bit because it comes in many guises. But they all boil down to “what monitor brightness or luminance level should I calibrate to?”

Monitor brightness is as critical as monitor colour when it comes to calibration.  If you look at previous articles on this blog you’ll see that I always quote the same calibration values, those being:

White Point: D65 – that figure takes care of colour.

Gamma: 2.2 – that value covers monitor contrast.

Luminance: 120 cdm2 (candelas per square meter) – that takes care of brightness.

Simple in’it….?!

However, when you’ve been around all this photography nonsense as long as I have you can overlook the possibility that people might not see things as being quite so blindingly obvious as you do.

And one of those ‘omissions on my part’ has been to do with monitor brightness settings COMBINED with working lighting levels in ‘the digital darkroom’.  So I suppose I’d better correct that failing on my part now.

What does a Monitor Profile Do for your image processing?

A correctly calibrated monitor and its .icc profile do a really simple but very mission-critical job.

If we open a new document in Photoshop and fill it with flat 255 white we need to see that it’s white.  If we hold an ND filter in front of our eye then the image won’t look white, it’ll look grey.

If we hold a blue filter in front of our eye the image will not look white – it’ll look blue.

That white image doesn’t exist ‘inside the monitor’ – it’s on our computer!  It only gets displayed on the monitor because of the graphics output device in our machine.

So, if you like, we’re on the outside looking in; and we are looking through a window on to our white image.  The colour and brightness level in our white image are correct on the inside of the system – our computer – but the viewing window or monitor might be too bright or too dark, and/or might be exhibiting a colour tint or cast.

Unless our monitor is a totally ‘clean window’ in terms of colour neutrality, then our image colour will not be displayed correctly.

And if the monitor is not running at the correct brightness then the colours and tones in our images will appear to be either too dark or too bright.  Please note the word ‘appear’…

Let’s get a bit fancy and make a greyscale in Photoshop:

monitor brightness,monitor calibration,monitor luminance,ColorMunki,i1 Display,spectrophotometer,colourimeter,ambient light,work space,photography,digital darkroom,Andy Astbury,Wildlife in Pixels,gamma,colour correction,image processing

The dots represent Lab 50 to Lab 95 – the most valuable tonal range between midtone and highlight detail.

Look at the distance between Lab 50 & Lab 95 on the three greyscales above – the biggest ‘span’ is the correctly calibrated monitor.  In both the ‘too bright & contrasty’ and the ‘too dark low contrast’ calibration, that valuable tonal range is compressed.

In reality the colours and tones in, say an unprocessed RAW file on one of our hard drives, are what they are.  But if our monitor isn’t calibrated correctly, what we ‘see’ on our monitor IS NOT REALITY.

Reality is what we need – the colours and tones in our images need to be faithfully reproduced on our monitor.

And so basically a monitor profile ensures that we see our images correctly in terms of colour and brightness; it ensures that we look at our images through a clean window that displays 100% of the luminance being sent to it – not 95% and not 120% – and that all our primary colours are being displayed with 100% fidelity.

In a nutshell, on an uncalibrated monitor, an image might look like crap, when in reality it isn’t.  The shit really starts to fly when you start making adjustments in an uncalibrated workspace – what you see becomes even further removed from reality.

“My prints come out too dark Andy – why?”

Because your monitor is too bright – CALIBRATE it!

“My pics look great on my screen, but everyone on Nature Photographers Network keeps telling me they’ve got too much contrast and they need a levels adjustment.  One guy even reprocessed one – everyone thought his version was better, but frankly it looked like crap to me – why is this happening Andy?

“Because your monitor brightness is too low but your gamma is too high – CALIBRATE it!  If you want your images to look like mine then you’ve got to do ALL the things I do, not just some of ’em – do you think I do all this shit for fun??????????……………grrrrrrr….

But there’s a potential problem;  just because your monitor is calibrated to perfection, that does NOT mean that everything will be golden from this point on

Monitor Viewing Conditions

So we’re outside taking a picture on a bright sunny day, but we can’t see the image on the back of the camera because there’s too much daylight, and we have to dive under a coat with our camera to see what’s going on.

But if we review that same image on the camera in the dark then it looks epic.

Now you have all experienced that…….

The monitor on the back of your camera has a set brightness level – if we view the screen in a high level of ambient light the image looks pale, washed out and in a general state of ultra low contrast.  Turn the ambient light down and the image on the camera screen becomes more vivid and the contrast increases.

But the image hasn’t changed, and neither has the camera monitor.

What HAS changed is your PERCEPTION of the colour and luminance values contained within the image itself.

Now come on kids – join the dots will you!

It does not matter how well your monitor is calibrated, if your monitor viewing conditions are not within specification.

Just like with your camera monitor, if there is too much ambient light in your working environment then your precisely calibrated monitor brightness and gamma will fail to give you a correct visualization or ‘perception’ of your image.

And the problems don’t end there either; coloured walls and ceilings reflect that colour onto the surface of your monitor, as does that stupid luminous green shirt you’re wearing – yes, I can see you!  And if you are processing on an iMac then THAT problem just got 10 times worse because of the glossy screen!

Nope – bead-blasting your 27 inches of Apple goodness is not the answer!

Right, now comes the serious stuff, so READ, INGEST and ACT.

ISO Standard 3664:2009 is the puppy we need to work to (sort of) – you can actually go and purchase this publication HERE should you feel inclined to dump 138 CHF on 34 pages of light bedtime reading.

There are actually two ISO standards that are relevant to us as image makers; ISO 12646:2015(draft) being the other.

12646 pertains to digital image processing where screens are to be compared to prints side by side (that does not necessarily refer to ‘desktop printer prints from your Epson 3000’).

3664:2009 applies to digital image processing where screen output is INDEPENDENT of print output.

We work to this standard (for the most part) because we want to process for the web as well as for print.

If we employ a print work flow involving modern soft-proofing and otherwise keep within the bounds of 3664 then we’re pretty much on the dance-floor.

ISO 3664 sets out one or two interesting and highly critical working parameters:

Ambient Light White Point: D50 – that means that the colour temperature of the light in your editing/working environment should be 5000Kelvin (not your monitor) – and in particular this means the light FALLING ON TO YOUR MONITOR from within your room. So room décor has to be colour neutral as well as the light source.

Ambient Light Value in your Editing Area: 32 to 64 Lux or lower.  Now this is what shocks so many of you guys – lower than 32 lux is basically processing in the dark!

Ambient Light Glare Permissible: 0 – this means NO REFLECTIONS on your monitor and NO light from windows or other light sources falling directly on the monitor.

Monitor White Point – D65 (under 3664) and D50 (under 12646) – we go with D65.

Monitor Luminance – 75 to 100 cdm2 (under 3664) and 80 to 120 cdm2 (under 12646 – here we begin to deviate from 3664.

We appear to be dealing with mixed reference units, but 1 Lux = 1 cdm2 or 1 candela per square metre.

The way Monitor Brightness or Luminance relates to ambient light levels is perhaps a little counter-intuitive for some folk.  Basically the LOWER your editing area Lux value the LOWER your Monitor Brightness or luminance needs to be.

Now comes the point in the story where common sense gets mixed with experience, and the outcome can be proved by looking at displayed images and prints; aesthetics as opposed numbers.

Like all serious photographers I process my own images on a wide-gamut monitor, and I print on a wide-gamut printer.

Wide gamut monitors display pretty much 90% to100% of the AdobeRGB1998 colour space.

What we might refer to as Standard Gamut monitors display something a little larger than the sRGB colour space, which as we know is considerably smaller than AdobeRGB1998.

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Left is a standard gamut/sRGB monitor and right is a typical wide gamut/AdobeRGB1998 monitor – if you can call any NEC ‘typical’!

Find all the gory details about monitors on this great resource site – TFT Central.

At workshops I process on a 27 inch non-Retina iMac – this is to all intents and purposes a ‘standard gamut’ monitor.

I calibrate my monitors with a ColorMunki Photo – which is a spectrophotometer.  Spectro’s have a tendency to be slow, and slightly problematic in the very darkest tones and exhibit something of a low contrast reaction to ‘blacks’ below around Lab 6.3 (RGB 20,20,20).

If you own a ColorMunki Display or i1Dispaly you do NOT own a spectro, you own a colorimeter!  A very different beast in the way it works, but from a colour point of view they give the same results as a spectro of the same standard – plus, for the most part, they work faster.

However, from a monitor brightness standpoint, they differ from spectros in their slightly better response to those ultra-dark tones.

So from a spectrophotometer standpoint I prefer to calibrate to ISO 12646 standard of 120cdm2 and control my room lighting to around 35-40 Lux.

Just so that you understand just how ‘nit-picking’ these standards are, the difference between 80cdm2 and 120 cdm2 is just 1/2 or 1/3rd of a stop Ev in camera exposure terms, depending on which way you look at it!

However, to put this monitor brightness standard into context, my 27 inch iMac came from Apple running at 290 cdm2 – and cranked up fully it’ll thump out 340 cdm2.

Most stand-alone monitors you buy, especially those that fall under the ‘standard gamut’ banner, will all be running at massively high monitor brightness levels and will require some severe turning down in the calibration process.

You will find that most monitor tests and reviews are done with calibration to the same figures that I have quoted – D65, 120cdm2 and Gamma 2.2 – in fact this non-standard set up has become so damn common it is now ‘standard’ – despite what the ISO chaps may think.

Using these values, printing out of Lightroom for example, becomes a breeze when using printer profiles created to the ICC v2 standard as long as you ‘soft proof’ the image in a fit and proper manner – that means CAREFULLY, take your time.  The one slight shortcoming of the set up is that side by side print/monitor comparisons may look ever so slightly out of kilter because of the D65 monitor white point – 6,500K transmitted white point as opposed to a 5,000K reflective white point.  But a shielded print-viewer should bring all that back into balance if such a thing floats your boat.

But the BIG THING you need to take away from the rather long article is the LOW LUX VALUE of you editing/working area ambient illumination.

Both the ColorMunki Photo and i1Pro2 spectrophotometers will measure your ambient light, as will the ColorMunki Display and i1 Display colorimeters, to name but a few.

But if you measure your ambient light and find the device gives you a reading of more than 50-60 lux then DO NOT ask the device to profile for your ambient light; in fact I would not recommend doing this AT ALL, here’s why.

I have a main office light that is colour corrected to 5000K and it chucks out 127 Lux at the monitor.  If I select the ‘measure and calibrate to ambient’ option on the ColorMunki Photo it eventually tells me I need a monitor brightness or luminance of 80 cdm2 – the only problem is that it gives me the same figure if I drop the ambient lux value to 100.

Now that smells a tad fishy to me……..

So my advice to anyone is to remove the variables, calibrate to 120 cdm2 and work in a very subdued ambient condition of 35 to 40 Lux. I find it easier to control my low lux working ambient light levels than bugger about with over-complex calibration.

To put a final perspective on this figure there is an interesting page on the Apollo Energytech website which quotes lux levels that comply with the law for different work environments – don’t go to B&Q or Walmart to do a spot of processing, and we’re all going to end up doing hard time at Her Madges Pleasure –  law breakers that we are!

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Colormunki Photo Update

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Colormunki Photo Update

Both my MacPro and non-retina iMac used to be on Mountain Lion, or OSX 10.8, and nope, I never updated to Mavericks as I’d heard so many horror stories, and I basically couldn’t be bothered – hey, if it ain’t broke don’t fix it!

But, I wanted to install CapOne Pro on the iMac for the live-view capabilities – studio product shot lighting training being the biggest draw on that score.

So I downloaded the 60 day free trial, and whadyaknow, I can’t install it on anything lower than OSX 10.9!

Bummer thinks I – and I upgrade the iMac to OSX 10.10 – YOSEMITE.

Now I was quite impressed with the upgrade and I had no problems in the aftermath of the Yosemite installation; so after a week or so muggins here decided to do the very same upgrade to his late 2009 Mac Pro.

OHHHHHHH DEARY ME – what a pigs ear of a move that turned out to be!

Needless to say, I ended up making a Yosemite boot installer and setting up on a fresh HDD.  After re-installing all the necessary software like Lightroom and Photoshop, iShowU HD Pro and all the other crap I use, the final task arrived of sorting colour management out and profiling the monitors.

So off we trundle to X-Rite and download the Colormunki Photo software – v1.2.1.  I then proceeded to profile the 2 monitors I have attached to the Mac Pro.

Once the colour measurement stage got underway I started to think that it was all looking a little different and perhaps a bit more comprehensive than it did before.  Anyway, once the magic had been done and the profile saved I realised that I had no way of checking the new profile against the old one – t’was on the old hard drive!

So I go to the iMac and bring up the Colormunki software version number – 1.1.1 – so I tell the software to check for updates – “non available” came the reply.

Colormunki software downloads

Colormunki software downloads

Colormunki v1.2.1 for Yosemite

Colormunki v1.2.1 for Yosemite

So I download 1.2.1, remove the 1.1.1 software and restart the iMac as per X-Rites instructions, and then install said 1.2.1 software.

Once installation was finished I profiled the iMac and found something quite remarkable!

Check out the screen grab below:

iMac screen profile comparrisons.

iMac screen profile comparisons. You need to click this to open full size in a new tab.

On the left is a profile comparison done in the ColourThink 2-D grapher, and on the right one done in the iMacs own ColourSynch Utility.

In the left image the RED gamut projection is the new Colormunki v1.2.1 profile. This also corresponds to the white mesh grid in the Colour Synch image.

Now the smaller WHITE gamut projection was produced with an i1Pro 2 using the maximum number of calibration colours; this corresponds to the coloured projection in the Coloursynch window image.

The GREEN gamut projection is the supplied iMac system monitor profile – which is slightly “pants” due to its obvious smaller size.

What’s astonished me is that the Colormunki Photo with the new software v1.2.1 has produced a larger gamut for the display than the i1 Pro 2 did under Mountain Lion OSX 10.8

I’ve only done a couple of test prints via softproofing in Lightroom, but so far the new monitor profile has led to a small improvement in screen-to-print matching of the some subtle yellow-green and green-blue mixes, aswell as those yellowish browns which I often found tricky to match when printing from the iMac.

So, my advice is this, if you own a Colormunki Photo and have upgraded your iMac to Yosemite CHECK your X-Rite software version number. Checking for updates doesn’t always work, and the new 1.2.1 Mac version is well worth the trouble to install.

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Camera Calibration

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Custom Camera Calibration

The other day I had an email fall into my inbox from leading UK online retailer…whose name escapes me but is very short… that made my blood pressure spike.  It was basically offering me 20% off the cost of something that will revolutionise my photography – ColorChecker Passport Camera Calibration Profiling software.

I got annoyed for two reasons:

  1. Who the “f***” do they think they’re talking to sending ME this – I’ve forgotten more about this colour management malarkey than they’ll ever know….do some customer research you idle bastards and save yourselves a mauling!
  2. Much more importantly – tens of thousands of you guys ‘n gals will get the same email and some will believe the crap and buy it – and you will get yourselves into the biggest world of hurt imaginable!

Don’t misunderstand me, a ColorChecker Passport makes for a very sound purchase indeed and I would not like life very much if I didn’t own one.  What made me seethe is the way it’s being marketed, and to whom.

Profile all your cameras for accurate colour reproduction…..blah,blah,blah……..

If you do NOT fully understand the implications of custom camera calibration you’ll be in so much trouble when it comes to processing you’ll feel like giving up the art of photography.

The problems lie in a few areas:

First, a camera profile is a SENSOR/ASIC OUTPUT profile – think about that a minute.

Two things influence sensor/asic output – ISO and lens colour shift – yep. that’s right, no lens is colour-neutral, and all lenses produce colour shifts either by tint or spectral absorption. And higher ISO settings usually produce a cooler, bluer image.

Let’s take a look at ISO and its influence on custom camera calibration profiling – I’m using a far better bit of software for doing the job – “IN MY OPINION” – the Adobe DNG Profile Editor – free to all MAC download and Windows download – but you do need the ColorChecker Passport itself!

I prefer the Adobe product because I find the ColorChecker software produced camera calibration profiles there were, well, pretty vile in terms of increased contrast especially; not my cup of tea at all.

camera calibration, Andy Astbury, colour, color management

5 images shot at 1 stop increments of ISO on the same camera/lens combination.

Now this is NOT a demo of software – a video tutorial of camera profiling will be on my next photography training video coming sometime soon-ish, doubtless with a somewhat verbose narrative explaining why you should or should not do it!

Above, we have 5 images shot on a D4 with a 24-70 f2.8 at 70mm under a consistent overcast daylight at 1stop increments of ISO between 200 and 3200.

Below, we can see the resultant profile and distribution of known colour reference points on the colour wheel.

camera calibration, Andy Astbury, colour, color management

Here’s the 200 ISO custom camera calibration profile – the portion of interest to us is the colour wheel on the left and the points of known colour distribution (the black squares and circled dot).

Next, we see the result of the image shot at 3200 ISO:

camera calibration, Andy Astbury, colour, color management

Here’s the result of the custom camera profile based on the shot taken at 3200 ISO.

Now let’s super-impose one over t’other – if ISO doesn’t matter to a camera calibration profile then we should see NO DIFFERENCE………….

camera calibration, Andy Astbury, colour, color management

The 3200 ISO profile colour distribution overlaid onto the 200 ISO profile colour distribution – it’s different and they do not match up.

……..well would you bloody believe it!  Embark on custom camera calibration  profiling your camera and then apply that profile to an image shot with the same lens under the same lighting conditions but at a different ISO, and your colours will not be right.

So now my assertions about ISO have been vindicated, let’s take a look at skinning the cat another way, by keeping ISO the same but switching lenses.

Below is the result of a 500mm f4 at 1000 ISO:

camera calibration, Andy Astbury, colour, color management

Profile result of a 500mm f4 at 1000 ISO

And below we have the 24-70mm f2.8 @ 70mm and 1000 ISO:

camera calibration, Andy Astbury, colour, color management

Profile result of a 24-70mm f2.8 @ 70mm at 1000 ISO

Let’s overlay those two and see if there’s any difference:

camera calibration, Andy Astbury, colour, color management

Profile results of a 500mm f4 at 1000 ISO and the 24-70 f2.8 at 1000 ISO – as massively different as day and night.

Whoops….it’s all turned to crap!

Just take a moment to look at the info here.  There is movement in the orange/red/red magentas, but even bigger movements in the yellows/greens and the blues and blue/magentas.

Because these comparisons are done simply in Photoshop layers with the top layer at 50% opacity you can even see there’s an overall difference in the Hue and Saturation slider values for the two profiles – the 500mm profile is 2 and -10 respectively and the 24-70mm is actually 1 and -9.

The basic upshot of this information is that the two lenses apply a different colour cast to your image AND that cast is not always uniformly applied to all areas of the colour spectrum.

And if you really want to “screw the pooch” then here’s the above comparison side by side with with  the 500f4 1000iso against the 24-70mm f2.8 200iso view:

camera calibration, Andy Astbury, colour, color management

500mm f4/24-70mm f2.8 1000 ISO comparison versus 500mm f4 1000 ISO and 24-70mm f2.8 200 ISO.

A totally different spectral distribution of colour reference points again.

And I’m not even going to bother showing you that the same camera/lens/ISO combo will give different results under different lighting conditions – you should by now be able to envisage that little nugget yourselves.

So, Custom Camera Calibration – if you do it right then you’ll be profiling every body/lens combo you have, at every conceivable ISO value and lighting condition – it’s one of those things that if you don’t do it all then you’d be best off not doing at all in most cases.

I can think of a few instances where I would do it as a matter of course, such as scientific work, photo-microscopy, and artwork photography/copystand work etc, but these would be well outside the remit the more normal photographic practices.

As I said earlier, the Passport device itself is worth far more than it’s weight in gold – set up and light your shot and include the Passport device in a prominent place. Take a second shot without it and use shot 1 to custom white balance shot 2 – a dead easy process that makes the device invaluable for portrait and studio work etc.

But I hope by now you can begin to see the futility of trying to use a custom camera calibration profile on a “one size fits all” basis – it just won’t work correctly; and yet for the most part this is how it’s marketed – especially by third party retailers.

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Paper White – Desktop Printing 101

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Paper White video

A while back I posted an article called How White is Paper White

As a follow-up to my last post on the basic properties of printing paper media I thought I’d post this video to refresh the idea of “white”.

In this video we basically look at a range of 10 Permajet papers and simply compare their tints and brightness – it’s an illustration I give at my print workshops which never fails to amaze all the attendees.

I know I keep ‘banging on’ about this but you must understand:

  • Very few paper whites are even close to being neutral.
  • No paper is WHITE in terms of luminosity – RGB 255 in 8 bit colour terms.
  • No paper can hold a true black – RGB 0 in 8 bit colour terms.

In real-world terms ALL printing paper is a TINTED GREY – some cool, some warm.

printing,paper white,desktop printing,Andy Astbury,Wildlife in Pixels

If we attempted to print the image above on a cool tinted paper then we would REDUCE or even CANCEL OUT the warm tonal effects and general ‘atmosphere’ of the image.

Conversely, print it to a warmer tinted ‘paper white’ and the atmosphere would be enhanced.

Would this enhancement be a good thing?  Well, er NO – not if we were happy with our original ‘on screen’ processing.

You need to look upon ‘paper white’ as another TOOL to help you achieve your goal of great looking photographs, with a minimum of fuss and effort on your part.

We have to ‘soft proof’ our images if we want to get a print off the printer that matches what we see on our monitor.

But we can’t soft proof until we have made a decision about what paper we are going to soft-proof to.

Choosing a paper who’s characteristics match our finished ‘on screen’ image in terms of TINT especially, will make the job of soft proofing much easier.

How, why?

Proper soft proofing requires us to make a copy of our original image (there’s most peoples first mistake – not making a copy) and then making adjustments to said copy, in a soft proof environment, so that it it renders correctly on the print – in other words it matches our original processed image.

Printing from Photoshop requires a hard copy, printing from Lightroom is different – it relies on VIRTUAL copies.

Either way, this copy and its proof adjustments are what get sent to the printer along what we call the PRINT PIPELINE.

The print pipeline has to do a lot of work:

  • It has to transpose our adjusted/soft proofed image colour values from additive RGB to print CMYK
  • It has to up sample or interpolate the image dpi instructions to the print head, depending on print output size.
  • It has to apply the correct droplet size instructions to each nozzle in the print head hundreds of times per second.
  • And it has to do a lot of other ‘stuff’ besides!!

The key component is the Printer Driver – and printer drivers are basically CRAP at carrying out all but the simplest of instructions.

In other words they don’t like hard work.

Printing to a paper white that matches our image:

  • Warm image to warm tint paper white
  • Cool image to cool paper white

will reduce to the amount of adjustments we have to make under soft proofing and therefore REDUCE the printer driver workload.

The less work the print driver has to do, the lower is the risk of things  ‘getting lost in translation‘ and if nothing gets lost then the print matches the on screen image – assuming of course that your eyes haven’t let you down at the soft proofing stage!

print,desktop printing,paper white

IMPORTANT – Click Image to Enlarge in new window

If we try to print this squirrel on the left to Permajet Gloss 271 (warmish image to very cool tint paper white) we can see what will happen.

We have got to make a couple of tweaks in terms on luminosity BUT we’ve also got to make a global change to the overall colour temperature of the image – this will most likely present us with a need for further  opposing colour channel adjustments between light and dark tones.

 

print,desktop printing,paper white

IMPORTANT – Click Image to Enlarge in new window

Whereas the same image sent to Permajet Fibre Base Gloss Warmtone all we’ll have to do is tweak the luminosity up a tiny bit and saturation down a couple of points and basically we’ll be sorted.

So less work, and less work means less room for error in our hardware drivers; this leads to more efficient printing and reduced print production costs.

And reduced cost leads to a happy photographer!

Printing images is EASY –  as long as you get all your ducks in a row – and you’ve only got a handful of ducks to control.

Understanding print media and grasping the implications of paper white is one of those ducks………

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Desktop Printing 101

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Understanding Desktop Printing – part 1

 

desktop printingDesktop printing is what all photographers should be doing.

Holding a finished print of your epic image is the final part of the photographic process, and should be enjoyed by everyone who owns a camera and loves their photography.

But desktop printing has a “bad rap” amongst the general hobby photography community – a process full of cost, danger, confusion and disappointment.

Yet there is no need for it to be this way.

Desktop printing is not a black art full of ‘ju-ju men’ and bear-traps  – indeed it’s exactly the opposite.

But if you refuse to take on board a few simple basics then you’ll be swinging in the wind and burning money for ever.

Now I’ve already spoken at length on the importance of monitor calibration & monitor profiling on this blog HERE and HERE so we’ll take that as a given.

But in this post I want to look at the basic material we use for printing – paper media.

Print Media

A while back I wrote a piece entitled “How White is Paper White” – it might be worth you looking at this if you’ve not already done so.

Over the course of most of my blog posts you’ll have noticed a recurring undertone of contrast needs controlling.

Contrast is all about the relationship between blacks and whites in our images, and the tonal separation between them.

This is where we, as digital photographers, can begin to run into problems.

We work on our images via a calibrated monitor, normally calibrated to a gamma of 2.2 and a D65 white point.  Modern monitors can readily display true black and true white (Lab 0 to Lab 100/RGB 0 to 255 in 8 bit terms).

Our big problem lies in the fact that you can print NEITHER of these luminosity values in any of the printer channels – the paper just will not allow it.

A papers ability to reproduce white is obviously limited to the brightness and background colour tint of the paper itself – there is no such think as ‘white’ paper.

But a papers ability to render ‘black’ is the other vitally important consideration – and it comes as a major shock to a lot of photographers.

Let’s take 3 commonly used Permajet papers as examples:

  • Permajet Gloss 271
  • Permajet Oyster 271
  • Permajet Portrait White 285

The following measurements have been made with a ColorMunki Photo & Colour Picker software.

L* values are the luminosity values in the L*ab colour space where 0 = pure black (0RGB) and 100 = pure white (255RGB)

Gloss paper:

  • Black/Dmax = 4.4 L* or 14,16,15 in 8 bit RGB terms
  • White/Dmin = 94.4 L* or 235,241,241 (paper white)

From these measurements we can see that the deepest black we can reproduce has an average 8bit RGB value of 15 – not zero.

We can also see that “paper white” has a leaning towards cyan due to the higher 241 green & blue RGB values, and this carries over to the blacks which are 6 points deficient in red.

Oyster paper:

  • Black/Dmax = 4.7 L* or 15,17,16 in 8 bit RGB terms
  • White/Dmin = 94.9 L* or 237,242,241 (paper white)

We can see that the Oyster maximum black value is slightly lighter than the Gloss paper (L* values reflect are far better accuracy than 8 bit RGB values).

We can also see that the paper has a slightly brighter white value.

Portrait White Matte paper:

  • Black/Dmax = 25.8 L* or 59,62,61 in 8 bit RGB terms
  • White/Dmin = 97.1 L* or 247,247,244 (paper white)

You can see that paper white is brighter than either Gloss or Oyster.

The paper white is also deficient in blue, but the Dmax black is deficient in red.

It’s quite common to find this skewed cool/warm split between dark tones and light tones when printing, and sometimes it can be the other way around.

And if you don’t think there’s much of a difference between 247,247,244 & 247,247,247 you’d be wrong!

The image below (though exaggerated slightly due to jpeg compression) effectively shows the difference – 247 neutral being at the bottom.

paper white,printing

247,247,244 (top) and 247,247,247 (below) – slightly exaggerated by jpeg compression.

See how much ‘warmer’ the top of the square is?

But the real shocker is the black or Dmax value:

paper,printing,desktop printing

Portrait White matte finish paper plotted against wireframe sRGB on L*ab axes.

The wireframe above is the sRGB colour space plotted on the L*ab axes; the shaded volume is the profile for Portrait White.  The sRGB profile has a maximum black density of 0RGB and so reaches the bottom of vertical L axis.

However, that 25.8 L* value of the matte finish paper has a huge ‘gap’ underneath it.

The higher the black L* value the larger is the gap.

What does this gap mean for our desktop printing output?

It’s simple – any tones in our image that are DARKER, or have a lower L* value than the Dmax of the destination media will be crushed into “paper black” – so any shadow detail will be lost.

Equally the same can be said for gaps at the top of the L* axis where “paper white” or Dmin is lower than the L* value of the brightest tones in our image – they too will get homogenized into the all-encompassing paper white!

Imagine we’ve just processed an image that makes maximum use of our monitors display gamut in terms of luminosity – it looks magnificent, and will no doubt look equally as such for any form of electronic/digital distribution.

But if we send this image straight to a printer it’ll look really disappointing, if only for the reasons mentioned above – because basically the image will NOT fit on the paper in terms of contrast and tonal distribution, let alone colour fidelity.
It’s at this point where everyone gives up the idea of desktop printing:

  • It looks like crap
  • It’s a waste of time
  • I don’t know what’s happened.
  • I don’t understand what’s gone wrong

Well, in response to the latter, now you do!

But do we have to worry about all this tech stuff ?

No, we don’t have to WORRY about it – that’s what a colour managed work flow & soft proofing is for.

But it never hurts to UNDERSTAND things, otherwise you just end up in a “monkey see monkey do” situation.

And that’s as dangerous as it can get – change just one thing and you’re in trouble!

But if you can ‘get the point’ of this post then believe me you are well on your way to understanding desktop printing and the simple processes we need to go through to ensure accurate and realistic prints every time we hit the PRINT button.

desktop printing

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Gamma Encoding – Under the Hood

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Gamma, Gamma Encoding & Decoding

Gamma – now there’s a term I see cause so much confusion and misunderstanding.

So many people use the term without knowing what it means.

Others get gamma mixed up with contrast, which is the worst mistake anyone could ever make!

Contrast controls the spatial relationship between black and white; in other words the number of grey tones.  Higher contrast spreads black into the darker mid tones and white into the upper mid tones.  In other words, both the black point and white point are moved.

The only tones that are not effected by changes in image gamma are the black point and white point – that’s why getting gamma mixed up with contrast is the mark of a “complete idiot” who should be taken outside and summarily shot before they have chance to propagate this shocking level of misunderstanding!

What is Gamma?

Any device that records an image does so with a gamma value.

Any device which displays/reproduces said image does so with a gamma value.

We can think of gamma as the proportional distribution of tones recorded by, or displayed on, a particular device.

Because different devices have different gamma values problems would arise were we to display an image that has a gamma of X on a display with a gamma of Y:

Ever wondered what a RAW file would look like displayed on a monitor without any fancy colour & gamma managed software such as LR or ACR?

gamma,gamma encoding,Andy Astbury

A raw file displayed on the back of the camera (left) and as it would look on a computer monitor calibrated to a gamma of 2.2 & without any colour & gamma management (right).

The right hand image looks so dark because it has a native gamma of 1.0 but is being displayed on a monitor with a native gamma of 2.2

RAW file Gamma

To all intents and purposes ALL RAW files have a gamma of 1.0

gamma,gamma encoding,Andy Astbury

Camera Sensor/Linear Gamma (Gamma 1.0)

Digital camera sensors work in a linear fashion:

If we have “X” number of photons striking a sensor photosite then “Y” amount of electrons will be generated.

Double the number of photons by doubling the amount of light, then 2x “Y” electrons will be generated.

Halve the number of photons by reducing the light on the scene by 50% then 0.5x “Y” electrons will be generated.

We have two axes on the graph; the horizontal x axis represents the actual light values in the scene, and the vertical y axis represents the output or recorded tones in the image.

So, if we apply Lab L* values to our graph axes above, then 0 equates to black and 1.0 equates to white.

The “slope” of the graph is a straight line giving us an equal relationship between values for input and output.

It’s this relationship between input and output values in digital imaging that helps define GAMMA.

In our particular case here, we have a linear relationship between input and output values and so we have LINEAR GAMMA, otherwise known as gamma 1.0.

Now let’s look at a black to white graduation in gamma 1.0 in comparison to one in what’s called an encoding gamma:

gamma,gamma encoding,Andy Astbury

Linear (top) vs Encoded Gamma

The upper gradient is basically the way our digital cameras see and record a scene.

There is an awful lot of information about highlights and yet the darker tones and ‘shadow’ areas are seemingly squashed up together on the left side of the gradient.

Human vision does not see things in the same way that a camera sensor does; we do not see linearly.

If the amount of ambient light falling on a scene suddenly doubles we will perceive the increase as an unquantifiable “it’s got brighter”; whereas our sensors response will be exactly double and very quantifiable.

Our eyes see a far more ‘perceptually even’ tonal distribution with much greater tonal separation in the darker tones and a more compressed distribution of highlights.

In other words we see a tonal distribution more like that contained in the gamma encoded gradient.

Gamma encoding can be best illustrated with another graph:

gamma,gamma encoding,Andy Astbury

Linear Gamma vs Gamma Encoding 1/2.2 (0.4545)

Now sadly this is where things often get misunderstood, and why you need to be careful about where you get information from.

The cyan curve is NOT gamma 2.2 – we’ll get to that shortly.

Think of the graph above as the curves panel in Lightroom, ACR or Photoshop – after all, that’s exactly what it is.

Think of our dark, low contrast linear gamma image as displayed on a monitor – what would we need to do to the linear slope  to improve contrast and generally brighten the image?

We’d bend the linear slope to something like the cyan curve.

The cyan curve is the encoding gamma 1/2.2.

There’s a direct numerical relationship between the two gamma curves; linear and 1/2.2. and it’s a simple power law:

  •  VO = VIγ where VO = output value, VI = input value and γ = gamma

Any input value (VI) on the linear gamma curve to the power of γ equals the output value of the cyan encoding curve; and γ as it works out equals 0.4545

  •  VI 0 = VO 0
  •  VI 0.25 = VO 0.532
  •  VI 0.50 = VO 0.729
  •  VI 0.75 = VO 0.878
  •  VI 1.0 = VO 1.0

Now isn’t that bit of maths sexy………………..yeah!

Basically the gamma encoding process remaps all the tones in the image and redistributes them in a non-linear ratio which is more familiar to our eye.

Note: the gamma of human vision is not really gamma 1/2.2 – gamma 0.4545.  It would be near impossible to actually quantify gamma for our eye due to the behavior of the iris etc, but to all intents and purposes modern photographic principles regard it as being ‘similar to’..

So the story so far equates to this:

gamma,gamma encoding,Andy Astbury

Gamma encoding redistributes tones in a non-linear manner.

But things are never quite so straight forward are they…?

Firstly, if gamma < 1 (less than 1) the encoding curve goes upwards – as does the cyan curve in the graph above.

But if gamma > 1 (greater than 1) the curve goes downwards.

A calibrated monitor has (or should have) a calibrated device gamma of 2.2:

gamma,gamma encoding,Andy Astbury

Linear, Encoding & Monitor gamma curves.

As you can now see, the monitor device gamma of 2.2 is the opposite of the encoding gamma – after all, the latter is the reciprocal of the former.

So what happens when we apply the decoding gamma/monitor gamma of 2.2 to our gamma encoded image?

gamma,gamma encoding,Andy Astbury

The net effect of Encode & Decode gamma – Linear.

That’s right, we end up back where we started!

Now, are you thinking:

  • Don’t understand?
  • We are back with our super dark image again?

Welcome to the worlds biggest Bear-Trap!

The “Learning Gamma Bear Trap”

Hands up those who are thinking this is what happens:

gamma,gamma encoding,Andy Astbury

If your arm so much as twitched then you are not alone!

I’ll admit to being naughty and leading you to edge of the pit containing the bear trap – but I didn’t push you!

While you’ve been reading this post have you noticed the occasional random bold and underlined text?

Them’s clues folks!

The super dark images – both seascape and the rope coil – are all “GAMMA 1.0 displayed on a GAMMA 2.2 device without any management”.

That doesn’t mean a gamma 1.0 RAW file actually LOOKS like that in it’s own gamma environment!

That’s the bear trap!

gamma,gamma encoding,Andy Astbury

Gamma 1.0 to gamma 2.2 encoding and decoding

Our RAW file actually looks quite normal in its own gamma environment (2nd from left) – but look at the histogram and how all those darker mid tones and shadows are piled up to the left.

Gamma encoding to 1/2.2 (gamma 0.4545) redistributes and remaps those all the tones and lightens the image by pushing the curve up BUT leaves the black and white points where they are.  No tones have been added or taken away, the operation just redistributes what’s already there.  Check out the histogram.

Then the gamma decode operation takes place and we end up with the image on the right – looks perfect and ready for processing, but notice the histogram, we keep the encoding redistribution of tones.

So, are we back where we started?  No.

Luckily for us gamma encoding and decoding is all fully automatic within a colour managed work flow and RAW handlers such as Lightroom, ACR and CapOnePro etc.

Image gamma changes are required when an image is moved from one RGB colour space to another:

  • ProPhoto RGB has a gamma of 1.8
  • Adobe RGB 1998 has a gamma of 2.2
  • sRGB has an oddball gamma that equates to an average of 2.2 but is nearly 1.8 in the deep shadow tones.
  • Lightrooms working colour space is ProPhoto linear, in other words gamma 1.0
  • Lightrooms viewing space is MelissaRGB which equates to Prophoto with an sRGB gamma.

Image gamma changes need to occur when images are sent to a desktop printer – the encode/decode characteristics are actually part and parcel of the printer profile information.

Gamma awareness should be exercised when it comes to monitors:

  • Most plug & play monitors are set to far too high a gamma ‘out the box’ – get it calibrated properly ASAP; it’s not just about colour accuracy.
  • Laptop screen gamma changes with viewing position – God they are awful!

Anyway, that just about wraps up this brief explanation of gamma; believe me it is brief and somewhat simplified – but hopefully you get the picture!

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Lightroom Tutorials #2

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Lightroom Tutorials,video,lessoneagle,golden eagle,snow,winter,Norway,wildlife

Image Processing in Lightroom & Photoshop

 

In this Lightroom tutorial preview I take a close look at the newly evolved Clone/Heal tool and dust spot removal in Lightroom 5.

This newly improved tool is simple to use and highly effective – a vast improvement over the great tool that it was already in Lightroom 4.

 

Lightroom Tutorials  Sample Video Link below: Video will open in a new window

 

https://vimeo.com/64399887

 

This 4 disc Lightroom Tutorials DVD set is available from my website at http://wildlifeinpixels.net/dvd.html

How White is Paper White?

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What is Paper White?

We should all know by now that, in RGB terms, BLACK is 0,0,0 and that WHITE is 255,255,255 when expressed in 8 bit colour values.

White can also be 32,768: 32,768: 32,768 when viewed in Photoshop as part of a 16 bit image (though those values are actually 15 bit – yet another story!).

Either way, WHITE is WHITE; or is it?

paper white,photo paper white,printing paper white,Permajet paper whites, snow, Arctic Fox

Arctic Fox in Deep Snow ©Andy Astbury/Wildlife in Pixels

Take this Arctic Fox image – is anything actually white?  No, far from it! The brightest area of snow is around 238,238,238 which is neutral, but it’s not white but a very light grey.  And we won’t even discuss the “whiteness” of  the fox itself.

paper white,photo paper white,printing paper white,Permajet paper whites, bird, pheasant, snow

Hen Pheasant in Snow ©Andy Astbury/Wildlife in Pixels

The Hen Pheasant above was shot very late on a winters afternoon when the sun was at a very low angle directly behind me – the colour temperature has gone through the roof and everything has taken on a very warm glow which adds to the atmosphere of the image.

paper white,photo paper white,printing paper white,Permajet paper whites, snow, sunset, extreme colour temperature

Extremes of colour temperature – Snow Drift at Sunset ©Andy Astbury/Wildlife in Pixels

We can take the ‘snow at sunset’ idea even further, where the suns rays strike the snow it lights up pink, but the shadows go a deep rich aquamarine blue – what we might call a ‘crossed curves’ scenario, where shadow and lower mid tones are at a low Kelvin temperature, and upper mid tones and highlights are at a much higher Kelvin.

All three of these images might look a little bit ‘too much’ – but try clicking one and viewing it on a darker background without the distractions of the rest of the page – GO ON, TRY IT.

Showing you these three images has a couple of purposes:

Firstly, to show you that “TRUE WHITE” is something you will rarely, if ever, photograph.

Secondly, viewing the same image in a different environment changes the eyes perception of the image.

The secondary purpose is the most important – and it’s all to do with perception; and to put it bluntly, the pack of lies that your eyes and brain lead you to believe is the truth.

Only Mother Nature, wildlife and cameras tell the truth!

So Where’s All This Going Andy, and What’s it got to do with Paper White?

Fair question, but bare with me!

If we go to the camera shop and peruse a selection of printer papers or unprinted paper samplers, our eyes tell us that we are looking at blank sheets of white paper;  but ARE WE?

Each individual sheet of paper appears to be white, but we see very subtle differences which we put down to paper finish.

But if we put a selection of, say Permajet papers together and compare them with ‘true RGB white’ we see the truth of the matter:

paper white,photo paper white,printing paper white,Permajet paper whites

Paper whites of a few Permajet papers in comparison to RGB white – all colour values are 8bit.

Holy Mary Mother of God!!!!!!!!!!!!!!!!

I’ll bet that’s come as a bit of a shocker………

No paper is WHITE; some papers are “warm”; and some are “cool”.

So, if we have a “warmish” toned image it’s going to be a lot easier to “soft proof” that image to a “warm paper” than a cool one – with the result of greater colour reproduction accuracy.

If we were to try and print a “cool” image on to “warm paper” then we’ve got to shift the whole colour balance of the image, in other words warm it up in order for the final print to be perceived as neutral – don’t forget, that sheet of paper looked neutral to you when you stuck it in the printer!

Well, that’s simple enough you might think, but you’d be very, very wrong…

We see colour on a print because the inks allow use to see the paper white through them, but only up to a point.  As colours and tones become darker on our print we see less “paper white” and more reflected colour from the ink surface.

If we shift the colour balance of the entire image – in this case warm it up – we shift the highlight areas so they match the paper white; but we also shift the shadows and darker tones.  These darker areas hide paper white so the colour shift in those areas is most definitely NOT desirable because we want them to be as perceptually neutral as the highlights.

What we need to do in truth is to somehow warm up the higher tonal values while at the same time keep the lowest tonal values the same, and then somehow match all the tones in between the shadows and highlights to the paper.

This is part of the process called SOFT PROOFING – but the job would be a lot easier if we chose to print on a paper whose “paper white” matched the overall image a little more closely.

The Other Kick in the Teeth

Not only are we battling the hue of paper white, or tint if you like, but we also have to take into account the luminance values of the paper – in other words just how “bright” it is.

Those RGB values of paper whites across a spread of Permajet papers – here they are again to save you scrolling back:

paper white,photo paper white,printing paper white,Permajet paper whites

Paper whites of a few Permajet papers in comparrison to RGB white – all colour values are 8bit.

not only tell us that there is a tint to the paper due to the three colour channel values being unequal, but they also tell us the brightest value we can “print” – in other words not lay any ink down!

Take Oyster for example; a cracking all-round general printer paper that has a very large colour gamut and is excellent value for money – Permajet deserve a medal for this paper in my opinion because it’s economical and epic!

Its paper white is on average 240 Red, 245 Green ,244 Blue.  If we have any detail in areas of our image that are above 240, 240, 240 then part of that detail will be lost in the print because the red channel minimum density (d-min) tops out at 240; so anything that is 241 red or higher will just not be printed and will show as 240 Red in the paper white.

Again, this is a problem mitigated in the soft proofing process.

But it’s also one of the reasons why the majority of photographers are disappointed with their prints – they look good on screen because they are being displayed with a tonal range of 0 to 255, but printed they just look dull, flat and generally awful.

Just another reason for adopting a Colour Managed Work Flow!

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