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:
- Panel Display Colour Bit Depth
- Panel Technology – IPS etc
- Monitor Panel Backlight – CCFL, WCCFL, LED etc
- Monitor Colour Look-Up Table – Monitor On-Board LUT (if applicable)
- Monitor connectivity
- 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!
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:
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:
VGA or D-Sub 15. Awful method of connection – went out with the Ark. If you are using this then “stop it”!
DVI – nothing wrong with this connection format whatsoever, but bare in mind it’s an 8 bit connection.
Dual Link DVI – still only 8 bit.
Displayport – 10 bit monitor input connection.
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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