Tag Archives: Adobe

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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Photoshop CC Update

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Photoshop CC Update

Installing a new Photoshop CC update is supposed to be a simple matter of clicking a button and the job gets done.

This morning both my Mac systems were telling me to update from v14.1.2 to v14.2

I have two Macs, a late 2012 iMac and a mid 2009 Mac Pro.  The Mac Pro used to run Snow Leopard but was upgraded to Mountain Lion because of Lightroom 5 dropping Snow Leopard support.

Now I never have any problems with Cloud Updates from Adobe on the iMac, but sometimes the Mac Pro can do some strange things – and this morning was no exception!

The update installed on the iMac without a hitch, but when the update was complete on the Mac Pro I was greeted with a message telling me that some components had not installed correctly.  On opening Photoshop CC I was greeted with the fact that the version had rolled back to v14.0 and that hitting UPDATE in both the app and my CC control panel simply informed me that my software was up to date and no updates were available!

So I just thought I’d do a blog entry on what to do if this ever happens to you!

 

Remove Photoshop CC

The first thing to do is UNINSTALL  Photoshop CC with the supplied uninstaller.

You’ll find this in the main Photoshop CC root directory:

Photoshop CC Update

Locate the Photoshop CC Uninstaller.

Take my advice and put a tick in the check box to “Remove Preferences” – the Photoshop preferences file can be a royal pain in the ass sometimes, so dump it – a new one will get written as soon as your fire Photoshop up after the new install.

Click UNINSTALL.

Once this action is complete YOU MUST RESTART THE MACHINE.

 

After the restart wait for the Creative Cloud to connect then open your CC control panel.

Under the Apps tab you’ll see that Photoshop CC is no longer listed.

Scroll down past all the apps Adobe have listed and you’ll come to Photoshop CC;  it’ll have an INSTALL button next to it – click the install button:

Photoshop CC Update

Install Photoshop CC from the Cloud control panel.

If you are installing the 14.1.2 to 14.2 update (the current one as of today’s date) you might find a couple of long ‘stick bits’ during the installation process – notably between 1 and 20% and a long one at 90% – just let the machine do it’s thing.

When the update is complete I’d recommend you do a restart – it might not be necessary, but I do it anyway.

Once the machine has restarted fire up Photoshop, click on ‘About Photoshop’ and you should see:

Photoshop CC Update

Photoshop “about screen” showing version number.

Because we dumped the preferences file we need to go and change the defaults for best best working practice:

Photoshop CC Update

Preferences Interface tab.

If you want to change the BG colour then do it here.

Next, click File Handling:

Photoshop CC Update

File handling tab in Photoshop Preferences

Remove the tick from the SAVE IN BACKGROUND check box – like the person who put it there, you too might think background auto-save is a good idea – IT ISN’T – think about it!

Finally, go to Performance:

Photoshop CC Update

Photoshop preferences Performance tab

and change the Scratch Disc to somewhere other than your system drive if you have the internal drives fitted.  If you only have 1 internal drive then leave “as is”.  You ‘could’ use an external drive as a scratch disk, but to be honest it really does need to be a fast drive over a fast connection – USB 2 to an old 250Gb portable isn’t really going to cut it!

You can go and check your Colour Settings, though these should not have changed – assuming you had ’em set right in the first place!

Here’s what they SHOULD look like:

Photoshop CC Update

Photoshop PROPER COLOUR SETTINGS!

That’s it – you’re done!

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If you find this post useful and informative please could you help by making a small donation – it would really help me out a lot – whatever you can afford would be gratefully received.

Your donation will help offset the costs of running this blog and so help me to bring you lots more useful and informative content.

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Pixel Resolution – part 2

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More on Pixel Resolution

In my previous post on pixel resolution  I mentioned that it had some serious ramifications for print.

The major one is PHYSICAL or LINEAR image dimension.

In that previous post I said:

  • Pixel dimension divided by pixel resolution = linear dimension

Now, as we saw in the previous post, linear dimension has zero effect on ‘digital display’ image size – here’s those two snake jpegs again:

Andy Astbury,wildlife in pixels,pixel,dpi,ppi,pixel resolution,photoshop,lightroom,adobe

European Adder – 900 x 599 pixels with a pixel resolution of 300PPI

Andy Astbury,wildlife in pixels,pixel,dpi,ppi,pixel resolution,photoshop,lightroom,adobe

European Adder – 900 x 599 pixels with a pixel resolution of 72PPI

Digital display size is driven by pixel dimension – NOT linear dimension or pixel resolution.

Print on the other hand is directly driven by image linear dimension – the physical length and width of our image in inches, centimeters or millimeters.

Now I teach this ‘stuff’ all the time at my Calumet workshops and I know it’s hard for some folk to get their heads around print size and printer output, but it really is simple and straightforward if you just think about it logically for minute.

Let’s get away from snakes and consider this image of a cute Red Squirrel:

Andy Astbury,wildlife in pixels,

Red Squirrel with Bushy Tail – what a cutey!
Shot with Nikon D4 – full frame render.

Yeah yeah – he’s a bit big in the frame for my taste but it’s a seller so boo-hoo – what do I know ! !

Shot on a Nikon D4 – the relevance of which is this:

  • The D4 has a sensor with a linear dimension of 36 x 24 millimeters, but more importantly a photosite dimension of 4928 x 3280. (this is the effective imaging area – total photosite area is 4992 x 3292 according to DXO Labs).

Importing this image into Lightroom, ACR, Bridge, CapOne Pro etc will take that photosite dimension as a pixel dimension.

They also attach the default standard pixel resolution of 300 PPI to the image.

So now the image has a set of physical or linear dimensions:

  • 4928/300  x  3280/300 inches  or  16.43″ x 10.93″

or

  • 417.24 x 277.71 mm for those of you with a metric inclination!

So how big CAN we print this image?

 

Pixel Resolution & Image Physical Dimension

Let’s get back to that sensor for a moment and ask ourselves a question:

  • “Does a sensor contain pixels, and can it have a PPI resolution attached to it?
  • Well, the strict answer would be No and No not really.

But because the photosite dimensions end up being ‘converted’ to pixel dimensions then let’s just for a moment pretend that it can.

The ‘effective’ PPI value for the D4 sensor could be easily derived from its long edge ‘pixel’ count of the FX frame divided by the linear length which is just shy of 36mm or 1.4″ – 3520 PPI or thereabouts.

So, if we take this all literally our camera captures and stores a file that has linear dimensions of  1.4″ x 0.9″, pixel dimensions of  4928 x 3280 and a pixel resolution of 3520 PPI.

Import this file into Lightroom for instance, and that pixel resolution is reduced to 300 PPI.  It’s this very act that renders the image on our monitor at a size we can work with.  Otherwise we’d be working on postage stamps!

And what has that pixel resolution done to the linear image dimensions?  Well it’s basically ‘magnified’ the image – but by how much?

 

Magnification & Image Size

Magnification factors are an important part of digital imaging and image reproduction, so you need to understand something – magnification factors are always calculated on the diagonal.

So we need to identify the diagonals of both our sensor, and our 300 PPI image before we can go any further.

Here is a table of typical sensor diagonals:

Andy Astbury

Table of Sensor Diagonals for Digital Cameras.

And here is a table of metric print media sizes:

Andy Astbury

Metric Paper Sizes including diagonals.

To get back to our 300 PPI image derived from our D4 sensor,  Pythagoras tells us that our 16.43″ x 10.93″ image has a diagonal of 19.73″ – or 501.14mm

So with a sensor diagonal of 43.2mm we arrive at a magnification factor of around 11.6x for our 300 PPI native image as displayed on our monitor.

This means that EVERYTHING on the sensor – photosites/pixels, dust bunnies, logs, lumps of coal, circles of confusion, Airy Discs – the lot – are magnified by that factor.

Just to add variety, a D800/800E produces native 300 PPI images at 24.53″ x 16.37″ – a magnification factor of 17.3x over the sensor size.

So you can now begin to see why pixel resolution is so important when we print.

 

How To Blow Up A Squirrel !

Let’s get back to ‘his cuteness’ and open him up in Photoshop:

Our Squirrel at his native 300 PPI open in Photoshop.

Our Squirrel at his native 300 PPI open in Photoshop.

See how I keep you on your toes – I’ve switched to millimeters now!

The image is 417 x 277 mm – in other words it’s basically A3.

What happens if we hit print using A3 paper?

Red Squirrel with Bushy Tail. D4 file at 300 PPI printed to A3 media.

Red Squirrel with Bushy Tail. D4 file at 300 PPI printed to A3 media.

Whoops – that’s not good at all because there is no margin.  We need workable margins for print handling and for mounting in cut mattes for framing.

Do not print borderless – it’s tacky, messy and it screws your printer up!

What happens if we move up a full A size and print A2:

Red Squirrel 300 PPI printed on A2

Red Squirrel D4 300 PPI printed on A2

Now that’s just over kill.

But let’s open him back up in Photoshop and take a look at that image size dialogue again:

Our Squirrel at his native 300 PPI open in Photoshop.

Our Squirrel at his native 300 PPI open in Photoshop.

If we remove the check mark from the resample section of the image size dialogue box (circled red) and make one simple change:

Our Squirrel at a reduced pixel resolution of 240 PPI open in Photoshop.

Our Squirrel at a reduced pixel resolution of 240 PPI open in Photoshop.

All we need to do is to change the pixel resolution figure from 300 PPI to 240 PPI and click OK.

We make NO apparent change to the image on the monitor display because we haven’t changed any physical dimension and we haven’t resampled the image.

All we have done is tell the print pipeline that every 240 pixels of this image must occupy 1 liner inch of paper – instead of 300 pixels per linear inch of paper.

Let’s have a look at the final outcome:

Red Squirrel D4 240 PPI printed on A2.

Red Squirrel D4 240 PPI printed on A2.

Perfick… as Pop Larkin would say!

Now we have workable margins to the print for both handling and mounting purposes.

But here’s the big thing – printed at 2880+ DPI printer output resolution you would see no difference in visual print quality.  Indeed, 240 PPI was the Adobe Lightroom, ACR default pixel resolution until fairly recently.

So there we go, how big can you print?? – Bigger than you might think!

And it’s all down to pixel resolution – learn to understand it and you’ll find a lot of  the “murky stuff” in photography suddenly becomes very simple!

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Pixel Resolution

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What do we mean by Pixel Resolution?

Digital images have two sets of dimensions – physical size or linear dimension (inches, centimeters etc) and pixel dimensions (long edge & short edge).

The physical dimensions are simple enough to understand – the image is so many inches long by so many inches wide.

Pixel dimension is straightforward too – ‘x’ pixels long by ‘y’ pixels wide.

If we divide the physical dimensions by the pixel dimensions we arrive at the PIXEL RESOLUTION.

Let’s say, for example, we have an image with pixel dimensions of 3000 x 2400 pixels, and a physical, linear dimension of 10 x 8 inches.

Therefore:

3000 pixels/10 inches = 300 pixels per inch, or 300PPI

and obviously:

2400 pixels/8 inches = 300 pixels per inch, or 300PPI

So our image has a pixel resolution of 300PPI.

 

How Does Pixel Resolution Influence Image Quality?

In order to answer that question let’s look at the following illustration:

Andy Astbury,pixels,resolution,dpi,ppi,wildlife in pixels

The number of pixels contained in an image of a particular physical size has a massive effect on image quality. CLICK to view full size.

All 7 square images are 0.5 x 0.5 inches square.  The image on the left has 128 pixels per 0.5 inch of physical dimension, therefore its PIXEL RESOLUTION is 2 x 128 PPI (pixels per inch), or 256PPI.

As we move from left to right we halve the number of pixels contained in the image whilst maintaining the physical size of the image – 0.5″ x 0.5″ – so the pixels in effect become larger, and the pixel resolution becomes lower.

The fewer the pixels we have then the less detail we can see – all the way down to the image on the right where the pixel resolution is just 4PPI (2 pixels per 0.5 inch of edge dimension).

The thing to remember about a pixel is this – a single pixel can only contain 1 overall value for hue, saturation and brightness, and from a visual point of view it’s as flat as a pancake in terms of colour and tonality.

So, the more pixels we can have between point A and point B in our image the more variation of colour and tonality we can create.

Greater colour and tonal variation means we preserve MORE DETAIL and we have a greater potential for IMAGE SHARPNESS.

REALITY

So we have our 3 variables; image linear dimension, image pixel dimension and pixel resolution.

In our typical digital work flow the pixel dimension is derived from the the photosite dimension of our camera sensor – so this value is fixed.

All RAW file handlers like Lightroom, ACR etc;  all default to a native pixel resolution of 300PPI. * (this 300ppi myth annoys the hell out of me and I’ll explain all in another post).

So basically the pixel dimension and default resolution SET the image linear dimension.

If our image is destined for PRINT then this fact has some serious ramifications; but if our image is destined for digital display then the implications are very different.

 

Pixel Resolution and Web JPEGS.

Consider the two jpegs below, both derived from the same RAW file:

Andy Astbury,pixels,resolution,dpi,ppi,Wildlife in Pixels

European Adder – 900 x 599 pixels with a pixel resolution of 300PPI

European Adder - 900 x 599 pixels with a pixel resolution of 72PPI

European Adder – 900 x 599 pixels with a pixel resolution of 72PPI

In order to illustrate the three values of linear dimension, pixel dimension and pixel resolution of the two images let’s look at them side by side in Photoshop:

Andy Astbury,photoshop,resolution,pixels,ppi,dpi,wildlife in pixels,image size,image resolution

The two images opened in Photoshop – note the image size dialogue contents – CLICK to view full size.

The two images differ in one respect – their pixel resolutions.  The top Adder is 300PPI, the lower one has a resolution of 72PPI.

The simple fact that these two images appear to be exactly the same size on this page means that, for DIGITAL display the pixel resolution is meaningless when it comes to ‘how big the image is’ on the screen – what makes them appear the same size is their identical pixel dimensions of 900 x 599 pixels.

Digital display devices such as monitors, ipads, laptop monitors etc; are all PIXEL DIMENSION dependent.  The do not understand inches or centimeters, and they display images AT THEIR OWN resolution.

Typical displays and their pixel resolutions:

  • 24″ monitor = typically 75 to 95 PPI
  • 27″ iMac display = 109 PPI
  • iPad 3 or 4 = 264 PPI
  • 15″ Retina Display = 220 PPI
  • Nikon D4 LCD = 494 PPI

Just so that you are sure to understand the implication of what I’ve just said – you CAN NOT see your images at their NATIVE 300 PPI resolution when you are working on them.  Typically you’ll work on your images whilst viewing them at about 1/3rd native pixel resolution.

Yes, you can see 2/3rds native on a 15″ MacBook Pro Retina – but who the hell wants to do this – the display area is minuscule and its display gamut is pathetically small. 😉

Getting back to the two Adder images, you’ll notice that the one thing that does change with pixel resolution is the linear dimensions.

Whilst the 300 PPI version is a tiny 3″ x 2″ image, the 72 PPI version is a whopping 12″ x 8″ by comparison – now you can perhaps understand why I said earlier that the implications of pixel resolution for print are fundamental.

Just FYI – when I decide I’m going to create a small jpeg to post on my website, blog, a forum, Flickr or whatever – I NEVER ‘down sample’ to the usual 72 PPI that get’s touted around by idiots and no-nothing fools as “the essential thing to do”.

What a waste of time and effort!

Exporting a small jpeg at ‘full pixel resolution’ misses out the unnecessary step of down sampling and has an added bonus – anyone trying to send the image direct from browser to a printer ends up with a print the size of a matchbox, not a full sheet of A4.

It won’t stop image theft – but it does confuse ’em!

I’ve got a lot more to say on the topic of resolution and I’ll continue in a later post, but there is one thing related to PPI that is my biggest ‘pet peeve’:

 

PPI and DPI – They Are NOT The Same Thing

Nothing makes my blood boil more than the persistent ‘mix up’ between pixels per inch and dots per inch.

Pixels per inch is EXACTLY what we’ve looked at here – PIXEL RESOLUTION; and it has got absolutely NOTHING to do with dots per inch, which is a measure of printer OUTPUT resolution.

Take a look inside your printer driver; here we are inside the driver for an Epson 3000 printer:

Andy Astbury,printer,dots per inch,dpi,pixels per inch,ppi,photoshop,lightroom,pixel resolution,output resoloution

The Printer Driver for the Epson 3000 printer. Inside the print settings we can see the output resolutions in DPI – Dots Per Inch.

Images would be really tiny if those resolutions were anything to do with pixel density.

It surprises a lot of people when they come to the realisation that pixels are huge in comparison to printer dots – yes, it can take nearly 400 printer dots (20 dots square) to print 1 square pixel in an image at 300 PPI native.

See you in my next post!

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Bit Depth

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Bit Depth – What is a Bit?

Good question – from a layman’s point of view it’s the smallest USEFUL unit of computer/digital information; useful in the fact that it can have two values – 0 or 1.

Think of it as a light switch; it has two positions – ON and OFF, 1 or 0.

bit, Andy Astbury, bit depth

A bit is like a light switch.

We have 1 switch (bit) with 2 potential positions (bit value 0 or 1) so we have a bit depth of 1. We can arrive at this by simple maths – number of switch positions to the power of the number of switches; in other words 2 to the 1st power.

How Does Bit Depth Impact Our Images:

So what would this bit depth of 1 mean in image terms:

Andy Astbury,bit depth,

An Image with a Bit Depth of 1 bit.

Well, it’s not going to win Wildlife Photographer of the Year is it!

Because each pixel in the image can only be black or white, on or off, 0 or 1 then we only have two tones we can use to describe the entire image.

Now if we were to add another bit to the overall bit depth of the image we would have 2 switches (bits) each with 2 potential values so the total number of potential values, so 2 to the 2nd, or 4 potential output values/tones.

Andy Astbury,bits,bit depth

An image with a bit depth of 2 bits.

Not brilliant – but it’s getting there!

If we now double the bit depth again, this time to 4 bit, then we have 2 to the 4th, or 16 potential tones or output values per image pixel:

Andy Astbury,bits,bit depth

A bit depth of 4 bits gives us 16 tonal values.

And if we double the bit depth again, up to 8 bit we will end up with 2 to the 8th power, or 256 tonal values for each image pixel:

Andy Astbury,bits,bit depth

A bit depth of 8 bits yields what the eye perceives to be continuous unbroken tone.

This range of 256 tones (0 to 255) is the smallest number of tonal values that the human eye can perceive as being continuous in nature; therefore we see an unbroken range of greys from black to white.

More Bits is GOOD

Why do we need to use bit depths HIGHER than 8 bit?

Our modern digital cameras capture and store RAW images to a bit depth of 12 bit, and now in most cases 14 bit – 4096 & 16,384 tonal values respectively.

Just as we use the ProPhotoRGB colour space to preserve as many CAPTURED COLOURS as we can, we need to apply a bit depth to our pixel-based images that is higher than the capture depth in order to preserve the CAPTURED TONAL RANGE.

It’s the “bigger bucket” or “more stairs on the staircase” scenario all over again – more information about a pixels brightness and colour is GOOD.

Andy Astbury,bits,bit depth,tonal range,tonality,tonal graduation

How Tonal Graduation Increases with Bit Depth.

Black is black, and white is white, but increased bit depth gives us a higher number of steps/tones; tonal graduations, to get from black to white and vice versa.

So, if our camera captures at 14 bit we need a 15 bit or 16 bit “bucket” to keep it in.  And for those who want to know why a 14 bit bucket ISN’T a good idea then try carrying 2 gallons of water in a 2 gallon bucket without spillage!

The 8 bit Image Killer

Below we have two identical grey scale images open in Photoshop – simple graduations from black to white; one is a 16 bit image, the other 8 bit:

Andy Astbury,bits,bit depth,tone,tonal graduation

16 bit greyscale at the top. 8 bit greyscale below – CLICK Image to view full size.

Now everything looks OK at this “fit to screen” magnification; and it doesn’t look so bad at 1:1 either, but let’s increase the magnification to 1600% so we can see every pixel:

 

Andy Astbury,bits,bit depth,tone,tonal range,tonal graduation

CLICK Image to view full size. At 1600% magnification we can see that the 8 bit file is degraded.

At this degree of magnification we can see a huge amount of image degradation in the lower, 8 bit image whereas the upper, 16 bit image looks tonally smooth in its graduation.

The degradation in the 8 bit image is simply due to the fact that the total number of tones is “capped” at 256. and 256 steps to get from the black to the white values of the image are not sufficient – this leaves gaps in the image that Photoshop has to fill with “invented” tonal information based on its own internal “logic”….mmmmmm….

There was a time when I thought “girlies” were the most illogical things on the planet; but since Photoshop, now I’m not so sure…!

The image is a GREYSCALE – RGB ratios are supposedly equal in every pixel, but as you can see, Photoshop begins to skew the ratios where it has to do its “inventing” so we not only have luminosity artifacts, but we have colour artifacts being generated too.

You might look upon this as “pixel peeping” and “geekey”, but when it comes to image quality, being a pixel-peeping Geek is never a bad thing.

Of course, we all know 8bit as being “jpeg”, and these artifacts won’t show up on a web-based jpeg for your website; but if you are in the business of large scale gallery prints, then printing from an 8 bit image file is never going to be a good idea as these artifacts WILL show on the final print.

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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

Colour Space & Profiles

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colour space

From Camera to Print
copyright 2013 Andy Astbury/Wildlife in Pixels

Colour space and device profiles seem to cause a certain degree of confusion for a lot of people; and a feeling of dread, panic and total fear in others!

The reality of colour spaces and device profiles is that they are really simple things, and that how and why we use them in a colour managed work flow is perfectly logical and easy to understand.

Up to a point colour spaces and device profiles are one and the same thing – they define a certain “volume” of colours from red to green to blue, and from black to white – and all the colours that lie in between those five points.

The colour spaces that most photographers are by now familiar with are ProPhotoRGB, AdobeRGB(1998) and sRGB – these are classed as “working colour spaces” and are standards of colour set by the International Color Consortium, or ICC; and they all have one thing in common; where red, green and blue are present in equal amounts the colour produced will be NEUTRAL.

The only real differences between these three working colour spaces is the “distances” between the five set points of red, green, blue, black and white.  The greater the distance between the three primary colours then the greater is the degree of graduation between them, hence the greater the number of potential colours.  In the diagram below we can see the sRGB & ProPhoto working colour spaces displayed on the same axes:

colour space volume

The sRGB & ProPhoto colour spaces. The larger volume of ProPhoto contains more colour variety between red, green & blue than sRGB.

If we were to mark five different points on the surface of a partially inflated balloon,  and then inflate it some more then the points in relation to the balloons surface would NOT change: the points remain the same.  But the spatial distances between the points would change, as would the internal volume.  It’s the same with our five points of colour reference – red, green, blue, black & white – they do NOT change between colour spaces; red is red no matter what the working colour space.  But the range of potential colours between our 5 points of reference increases due to increased colour space volume.

So now we have dealt with the basics of the three main working colour spaces, we need to consider the volume of colour our camera sensor can capture – if you like, its colour space; but I’d rather use the word “gamut”.

Let’s take the Canon 5DMk3 as an example, and look at the volume, or gamut, of colour that its sensor can capture, in direct comparison with our 3 quantifiable working colour spaces:

colour space

The Canon 5DMk3 sensor gamut (black) in comparison to ProPhoto (largest), AdobeRGB1998 & sRGB (smallest) working colour spaces.

In a previous blog article I wrote – see here – I mentioned how to setup the colour settings in Photoshop, and this is why.  If you want to keep the greatest proportion of your camera sensors captured colour then you need to contain the image within the ProPhotoRGB working colour space.  If you don’t, and you use AdobeRGB or sRGB as Photoshops working colour space then you will loose a certain proportion of those captured colours – as I’ve heard it put before, it’s like a sex change operation – certain colours get chopped off, and once that’s happened you can’t get them back!

To keep things really simple just think of the 3 standard working colour spaces as buckets – the bigger the bucket, the more colour it contains; and you can’t tip the colours captured by your camera into a smaller bucket without getting spillage and making a mess on the floor!

As I said before, working colour spaces are neutral; but seldom does our camera ever capture a scene that contains pure neutrals.  Even though an item in the scene may well be neutral in colour, camera sensors quite often skew these colours ever so slightly; most Canon RAW files always look a teeny-weeny ever so slight bit magenta to me when I import them; but there again I’m a Nikon shooter seem to have a minute greenish tinge to them before processing.

Throughout our imaging work flow we have 3 stages:

1. Input (camera or scanner).

2. Working Process (Lightroom, Photoshop etc).

3. Output (printer for example).

And each stage has its representative type of colour space – we have input profiles, working colour spaces and output profiles.

So we have our camera capture gamut (colour space if you like) and we’ve opened our image in Photoshop or Lightroom in the ProPhoto working colour space – there’s NO SPILLAGE!

We now come to the crux of colour management; before we can do anything else we need to profile our “window onto our image” – the monitor.

In order to see the reality of what the camera captured we need to ensure that our monitor is in line with our WORKING COLOUR SPACE in terms of colour neutrality – not that of the camera as some people seem to think.

All 3 working colour spaces posses the same degree of colour neutrality where red, green & blue are present at the same values irrespective of physical size of the colour space.

So as long as our monitor is profiled to be:

1. Accurately COLOUR NEUTRAL

2. Displaying maximum brightness only in the presence true white – which you’ll hardly ever photograph, even snow isn’t white.

then we will see a highly workable representation of image colour neutrality and luminosity on our monitor.  Only by working this way can we actually tell if the camera has captured the image correctly in terms of colour balance and overall exposure.

And the fact that our monitor CANNOT display all the colours contained within our big ProPhoto bucket is, to all intents and purposes,  a fairly mute point; though seeing as many of them as possible is never a bad thing.

And using a monitor that does NOT display the volume of colour approximating or exceeding that of the Adobe working space can be highly detrimental for the reasons discussed in my previous post.

Now that we’ve covered input profiles and working colour spaces we need to move on and outline the basics of output profiles, and printer profiles in particular.

colour space, profile, print profile

Adobe & sRGB working paces in comparison to the colours contained in the Kingfisher image and the profile for Permajet Oyster paper using the Epson 7900 printer. (CLICK image for full sized view).

In the image above we can see both the Adobe and sRGB working spaces and the full distribution of colours contained in the Kingfisher image which is a TIFF file in our big ProPhoto bucket of colour;  and a black trace which is the colour profile (or space if you like) for Permajet Oyster paper using Epson UltraChrome HDR ink on an Epson 7900 printer.

As we can see, some of the colours contained in the image fall outside the gamut of the sRGB working colour space; notably some oranges and “electric blues” which are basically colours of the subject and are most critical to keep in the print.

However, all those ProPhoto colours are capable of being reproduced on the Epson 7900 using Permajet Oyster paper because, as the black trace shows, the printer/ink/paper combination can reproduce colours that lie outside of the Adobe working colour space.

The whole purpose of that particular profile is to ensure that the print matches what we can see on the monitor both in terms of colour and brightness – in other words, what we see is what we get – WYSIWYG!

The beauty of a colour managed workflow is that it’s economical – assuming the image is processed correctly then printing via an accurate printer profile can give you a perfect printed rendition of your screen image using just a single sheet of paper – and only one sheets worth of ink.

colour space, colour profile

The difference between colour profiles for the same printer paper on different printers. Epson 3000 printer profile trace in Red (CLICK image for full size view).

If we were to switch printers to an Epson 3000 using UltraChrome K3 ink on the very same paper, the area circled in white shows us that there are a couple of orange hue colours that are a little problematic – they lie either close to or outside the colour gamut of this printer/ink/paper combination, and so they need to be changed in order to ‘fit’, either by localised adjustment or variation of rendering intent – but that’s a story for later!

Why is it different? Well, it’s not to do with the paper for sure, so it’s down to either the ink change or printer head.  Using the same K3 ink in an Epson 4800 brings the colours back into gamut, so the difference is in the printer head itself, or the printer driver, but as I said, it’s a small problem easily fixed.

When you consider the low cost of achieving an accurate monitor profile – see this previous post – and combine that with an accurate printer output profile or two to match your chosen printer papers, and then deploy these assets correctly you have a proper colour managed workflow.  Add to that the cost savings in ink and paper and it becomes a bit of a “no-brainer” doesn’t it?

In this post I set out to hopefully ‘demystify’ colour spaces and profiles in terms of what they are and how they are used – I hope I’ve succeeded!

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Monitor Calibration with ColorMunki

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Monitor Calibration with ColorMunki Photo

Following on from my previous posts on the subject of monitor calibration I thought I’d post a fully detailed set of instructions, just to make sure we’re all “singing from the same hymn sheet” so to speak.

Basic Setup

_D4R7794

Put the ColorMunki spectrophotometer into the cover/holder and attach the USB cable.

_D4R7798

Always keep the sliding dust cover closed when storing the ColorMunki in its holder – this prevents dust ingress which will effect the device performance.

BUT REMEMBER – slide the cover out of the way before you begin the calibration process!

colormunkiSpecCover

Install the ColorMunki software on your machine, register it via the internet, then check for any available updates.

Once the software is fully installed and working you are ready to begin.

Plug the USB cable into an empty USB port on your computer – NOT an external hub port as this can sometimes cause device/system communication problems.

Launch the ColorMunki software.

The VERY FIRST THING YOU NEED TO DO is open the ColorMunki software preferences and ensure that it looks like the following screen:

PC: File > Preferences

Mac: ColorMunki Photo > Preferences

Screen Shot 2013-10-17 at 11.28.32

The value for the Tone Response Curve MUST be set to 2.2 which is the default value.

The ICC Profile Version number MUST be set to v2 for best results – this is NOT the default.

Ensure the two check boxes are “ticked”.**

** These settings can be something of a contentious issue. DDC & LUT check boxes should only be “ticked” if your Monitor/Graphics card combination offers support for these modes.

If you find these settings make your monitor become excessively dark once profiling has been completed, start again ensuring BOTH check boxes are “unticked”.

Untick both boxes if you are working on an iMac or laptop as for the most part these devices support neither function.

For more information on this, a good starting point is a page on the X-Rite website available on the link below:

http://xritephoto.com/ph_product_overview.aspx?ID=1115&Action=Support&SupportID=5561

If you are going to use the ColorMunki to make printer profiles then ensure the ICC Profile Version is set to v2.

By default the ColorMunki writes profiles in ICC v4 – not all computer operating systems can function correctly from a graphics colour aspect; but they can all function perfectly using ICC v2.

You should only need to do this operation once, but any updates from X-Rite, or a re-installation of the software will require you to revisit the preferences panel just to check all is well.

Once this panel is set as above Click OK and you are ready to begin.

 

Monitor Calibration

This is the main ColorMunki GUI, or graphic user interface:

Screen Shot 2013-10-17 at 12.32.58

Click Profile My Display

Screen Shot 2013-10-17 at 11.17.49

Select the display you want to profile.

I use what is called a “double desktop” and have two monitors running side by side; if you have just a single monitor connected then that will be the only display you see listed.

Click Next>.

Screen Shot 2013-10-17 at 11.18.18

Select the type of display – we are talking here about monitor calibration of a screen attached to a PC or Mac so select LCD.

Laptops – it never hurts a laptop to be calibrated for luminance and colour, but in most cases the graphics output LUT (colour Look Up Table) is barely 8 bit to begin with; the calibration process will usually reduce that to less than 8 bit. This will normally result in the laptop screen colour range being reduced in size and you may well see “virtual” colour banding in your images.

Remedy: DON’T PROCESS ON A LAPTOP – otherwise “me and the boys” will be paying you a visit!

Select Advanced.

Deselect the ambient light measurement option – it can be expensive to set yourself up with proper lighting in order to have an ICC standard viewing/processing environment; daylight (D65) bulbs are fairly cheap and do go a long way towards helping, but the correct amount of light and the colour of the walls and ceiling, and the exclusion of extraneous light sources of incorrect colour temperature (eg windows) can prove somewhat more problematic and costly.

Processing in darkened room without light is by far the easiest, cheapest and most cost-effective way of obtaining correct working conditions.

Set the Luminance target Value to 120 (that’s 120 candelas per square meter if you’re interested!).

Set the Target White Point to D65 (that’s 6500 degrees Kelvin – mean average daylight).

Click Next>.

Screen Shot 2013-10-17 at 11.19.44

With the ColorMunki connected to your system this is the screen you will be greeted with.

You need to calibrate the device itself, so follow the illustration and rotate the ColorMunki dial to the indicated position.

Once the device has calibrated itself to its internal calibration tile you will see the displayed GUI change to:

Screen Shot 2013-10-17 at 11.20.26

Follow the illustration and return the ColorMunki dial to its measuring position.

Screen Shot 2013-10-17 at 11.20.49

Click Next>.

Screen Shot 2013-10-17 at 11.21.11

With the ColorMunki in its holder and with the spectrophotometer cover OPEN for measurement, place the ColorMunki on the monitor as indicated on screen and in the image below:

XR-CLRMNK-01

We are now ready to begin the monitor calibration.

Click Next>.

The first thing the ColorMunki does is measure the luminosity of the screen. If you get a manual adjustment prompt such as this (indicates non-support/disabling of DDC preferences option):

ColorMunki-Photo-display-screen-111

Simply turn adjust the monitor brightness slowly until the indicator line is level with the central datum line; you should see a “tick” suddenly appear when the luminance value of 120 is reached by your adjustments.

LCDs are notoriously slow to respond to changes in “backlight brightness” so make an adjustment and give the monitor a few seconds to settle down.

You may have to access your monitor controls via the screen OSD menu, or on Mac via the System Preferences > Display menu.

Once the Brightness/Luminance of the monitor is set correctly then ColorMunki will proceed will proceed with its monitor output colour measurements.

In order for you to understand monitor calibration and what is going on here is a sequence of slides from one of my workshops on colour management:

moncal1

moncal2

moncal3

moncal4

Once the measurements are complete the GUI will return to the screen in this form.

Screen Shot 2013-10-17 at 11.26.29

Either use the default profile name, or one of your own choice and click Save.

NOTE: Under NO CIRCUMSTANCES can you rename the profile after it has been saved, or any other .icc profile for that matter, otherwise the profile will not work.

Click Next>.

Screen Shot 2013-10-17 at 11.27.00

Click Save again to commit the new monitor profile to you operating system as the default monitor profile.

You can set the profile reminder interval from the drop down menu.

Click Next>.

Screen Shot 2013-10-17 at 12.32.58

Monitor calibration is now complete and you are now back to the ColorMunki startup GUI.

Quit or Exit the ColorMunki application – you are done!

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Screen Capture logos denoting ColorMunki & X-Rite are the copyright of X-Rite.

Monitor Calibration Devices

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Colour management is the simple process of maintaining colour accuracy and consistency between the ACTUAL COLOURS in your image, in terms of Hue, Saturation and Luminosity; and those reproduced on your RGB devices; in this case, displayed on your monitor. Each and every pixel in your image has its very own individual RGB colour values and it is vital to us as photographers that we “SEE” these values accurately displayed on our monitors.

If we were to visit The National Gallery and gaze upon Turners “Fighting Temeraire” we would see all those sumptuous colours on the canvass just as J.M.W. intended; but could we see the same colours if we had a pair of Ray Bans on?

No, we couldn’t; because the sunglasses behave as colour filters and so they would add a “tint” to every colour of light that passes through them.

What you need to understand about your monitor is that it behaves like a filter between your eyes and the recorded colours in your image; and unless that “filter” is 100% neutral in colour, then it will indeed “tint” your displayed image.

So, the first effect of monitor calibration is that the process NEUTRALIZES any colour tint in the monitor display and so shows us the “real colours” in our images; the correct values of Hue and Saturation.

Now imagine we have an old fashioned Kodak Ektachrome colour slide sitting in a projector. If we have the correct wattage bulb in the projector we will see the correct LUMINOSITY of the slide when it is projected.

But if the bulb wattage is too high then the slide will project too brightly, and if the bulb wattage is too low then the projected image will not be bright enough.

All our monitors behave just like a projector, and as such they all have a brightness adjustment which we can directly correlate to our old fashioned slide projector bulb, and this brightness, or backlight control is another aspect of monitor calibration.

Have you done a print that comes out DARKER than the image displayed on the screen?

If you have then your monitor backlight is too bright!

And so, the second effect of monitor calibration is the setting of the correct level of brightness or back lighting of our monitor in order for us to see the true Luminosity of the pixels in our images.

Without accurate Monitor Calibration your ability to control the accuracy of colour and overall brightness of your images is severely limited.

I get asked all the time “what’s the best monitor calibration device to use” so, above is a short video (no sound) I’ve made showing the 3D and 2D plots of profiles I’ve just made for the same monitor using teo different monitor calibration devices/spectrophotometers from opposite ends of the pricing scale.

The first plot you see in black is the AdobeRGB1998 working colour space – this is only shown as a standard by which you can judge the other two profiles; if you like, monitor working colour spaces.

The yellow plot that shows up as an overlay is a profile done with an Xrite ColourMunki Photo, which usually retails for around £300 – and it clearly shows this particular monitor rendering a greater number of colours in certain areas than are contained in the Adobe1998 reference space.

The cyan plot is the same monitor, but profiled with the i1Photo Pro 2 spectro – not much change out of £1300 thank you very much – and the resulting profile virtually an identical twin of the one obtained with the ColorMunki which retails for a quarter of the price!

Don’t get me wrong, the i1 is a far more efficient monitor calibration device if you want to produce custom PRINTER profiles as well, but if you are happy using OEM profiles and just want perfect monitor calibration then I’d say the ColorMunki Photo is the more sensible purchase; or better still the ColorMunki Display at only around £110.

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