Monitors and Color Bit Depth – yawn, yawn – Andy’s being boring again!
Well, perhaps I am, but I know ‘stuff’ you don’t – and I’m telling YOU that you need to know it if you want to get the best out of your photography – so there!
Let me begin by saying that NOTHING monitor-related has any effect on your captured images. But EVERYTHING monitor-related DOES have an effect on the way you SEE your images, and therefore definitely has an effect on your image adjustments and post-processing.
So anything monitor-related can have either a positive or negative effect on your final image output.
I’m going to begin with a somewhat disconnected analogy, but bare with me here.
We live in the ‘real and natural world’, and everything that we see around us is ANALOGUE. Nature exists on a natural curve and is full of infinite variation. In the digital world though, everything has to be put in a box.
We’ll begin with two dogs – a Labrador and a Poodle. In this instance both natural and digital worlds can cope with the situation, because nature just regards them for what they are, and digital can put the Labrador in a box named ‘Labrador’ and the Poodle in a separate box just for Poodles.
Let’s now imagine for a fleeting second that Mr. Lab and Miss Poodle ‘get jiggy’ with the result of dog number 3 – a Labradoodle. Nature just copes with the new dog because it sits on natures ‘doggy curve’ half way between Mum and Dad.
But digital is having a bloody hissy-fit in the corner because it can’t work out what damn box to put the new dog in. The only way we can placate digital is to give it another box, one for 50% Labrador and 50% Poodle.
Now if our Labradoodle grows up a bit then starts dating and makes out with another Labrador then we end up with a fourth dog that is 75% Labrador and 25% Poodle. Again, nature just takes all in her stride, but digital in now having a stroke because it’s got no box for that gene mix.
Every time we give digital a new box we have effectively given it a greater bit depth.
Now imagine this process of cross-breed gene dilution continues until the glorious day arrives when a puppy is born that is 99% Labrador and only 1% Poodle. It’ll be obvious to you that by this time digital has a flaming warehouse full of boxes that can cope with just about any gene mix, but alas, the last time bit depth was increased was to accommodate 98% Lab 2% Poodle.
Digital is by now quite old and grumpy and just can’t be arsed anymore, so instead of filling in triplicate forms to request a bit depth upgrade it just lumps our new dog in the same classification box as the previous one.
So our new dog is put in the wrong box.
Digital hasn’t been slap-dash though and put the pup in any old box, oh no. Digital has put the pup in the nearest suitable box – the box with the closest match to reality.
Please note that the above mentioned boxes are strictly metaphorical, and no puppies were harmed during the making of this analogy.
Digital images are made up of pixels, and a pixel can be thought of as a data point. That single data point contains information about luminance and colour. The precision of that information is determined by the bit depth of the data
Very little in our ‘real world’ has a surface that looks flat and uniform. Even a supposedly flat, uniform white wall on a building has subtle variations and graduations of colour and brightness/luminance caused by the angular direction of light and its own surface texture. That’s nature for you in the analogy above.
We are all familiar with RGB values for white being 255,255,255 and black being 0,0,0, but those are only 8 bit values.
8 bit allows for 256 discrete levels of information (or gene mix classification boxes for our Labradoodles), and a scale from 0 to 255 contains 256 values – think about it for a second!
At all bit depth values black is always 0,0,0 but white is another matter entirely:
8 bit = 256 discrete values so image white is 255,255,255
10 bit = 1,024 discrete values so image white is 1023,1023,1023
12 bit = 4,096 discrete values so image white is 4095,4095,4095
14 bit = 16,384 discrete values so image white is 16383,16383,16383
15 bit = 32,768 discrete values so image white is 32767,32767,32767
16 bit = 65,536 discrete values so image white should be 65535,65535,65535 – but it isn’t – more later!
And just for giggles here are some higher bit depth potentials:
24 bit = 16,777,216 discrete values
28 bit = 268,435,456 discrete values
32 bit = 4,294,967,296 discrete values
So you can see a pattern here. If we double the bit depth we square the value of the information, and if we halve the bit depth the information we are left with is the square root of what we started with.
And if we convert to a lower or smaller bit depth “digital has fewer boxes to put the different dogs in to, so Labradoodles of varying genetic make-ups end up in the same boxes. They are no longer sorted in such a precise manner”.
The same applies to our images. Where we had two adjacent pixels of slightly differing value in 16 bit, those same two adjacent pixels can very easily become totally identical if we do an 8 bit conversion and so we lose fidelity of colour variation and hence definition.
This is why we should archive our processed images as 16 bit TIFFS instead of 8 bit JPEGs!
In an 8 bit image we have black 0,0,0 and white 255,255,255 and ONLY 254 available shades or tones to graduate from one to the other.
Whereas, in a 16 bit image black is 0,0,0 and white is 65535,65535,65535 with 65,534 intervening shades of grey to make the same black to white transition:
But we have to remember that whatever the bit depth value is, it applies to all 3 colour channels:
So a 16 bit image should contain a potential of 65536 values per colour channel.
How Many Colours?
So how many colours can our bit depth describe Andy?
Simple answer is to cube the bit depth value, so:
8 bit = 256x256x256 = 16,777,216 often quoted as 16.7 million colours.
10 bit = 1024x1024x1024 = 1,073,741,824 or 1.07 billion colours or EXACTLY 64x the value of 8 bit!
16 bit = 65536x65536x65536 = 281,474,976,710,656 colours. Or does it?
Confusion Reigns Supreme
Now here’s where folks get confused.
Photoshop does not WORK in 16 bit, but in 15 bit + 1 level. Don’t believe me? Go New Document, RGB, 16 bit and select white as the background colour.
Open up your info panel, stick your cursor anywhere in the image area and look at the 16 bit RGB read out and you will see a value of 32768 for all 3 colour channels – that’s 15 bit folks! Now double the 32768 value – yup, that’s right, you get 16 bit or 65,536!
Why does Photoshop do this? Simple answer is ‘for speed’ – or so they say at Adobe! There are numerous others reasons that you’ll find on various forums etc – signed and unsigned integers, mid-points, float-points etc – but really, do we care?
Things are what they are, and rumor has it that once you hit the save button on a 16 bit TIFF is does actually save out at 16 bit.
So how many potential colours in 16 bit Photoshop? Dunno! But it’ll be somewhere between 35,184,372,088,832 and 281,474,976,710,656, and to be honest either value is plenty enough for me!
The second line of confusion usually comes from PC users under Windows, and the Windows 24 bit High Color and 32 bit True Color that a lot of PC users mistakenly think mean something they SERIOUSLY DO NOT!
Windows 24 bit means 24 bit TOTAL – in short, 8 bits per channel, not 24!
Windows 32 bit True Color is something else again. Correctly known as 32 bit RGBA it contains 4 channels of 8 bits each; three 8 bit colour channels and an 8 bit Alpha channel used for transparency.
The same 32 bit RGBA colour (Mac call it ARGB) has been utilised on Mac OS for ever, but most Mac users never questioned it because it’s not quite so obvious in OSX as it is in Windows unless you look at the Graphics/Displays section of your System report, and who the Hell ever goes there apart from twats like me:
Above you can see the pixel depth being reported as 32 bit colour ARGB8888 – that’s Apple-speak for Windows 32 bit True Colour RGBA. But like a lot of ‘things Mac’ the numbers give you the real information. The channels are ordered Alpha, Red, Green, Blue and the four ‘8’s give you the bit depth of each pixel, or as Apple put it ‘pixel depth’.
However, in the latter part of 2015 Apple gave OSX 10.11 El Capitan a 10 bit colour capability, though hardly anyone knew including ‘yours truly’. I never have understood why they kept it ‘on the down-low’ but there was no fan-fare that’s for sure.
Now you can see the pixel depth being reported as 30 bit ARGB2101010 – meaning that the transparency Alpha channel has been reduced from 8 bit to 2 bit and the freed-up 6 bits have been distributed evenly between the Red, Green and Blue colour channels.
Your computer has a maximum display bit depth output capability that is defined by:
- a. the operating system
- b. the GPU fitted
Your system might well support 10 bit colour, but will only output 8 bit if the GPU is limited to 8 bit.
Likewise, you could be running a 10 bit GPU but if your OS only supports 8 bit, then 8 bit is all you will get out of the system (that’s if the OS will support the GPU in the first place).
Monitors have their own panel display bit depth, and panel bit depth costs money.
A lot of LCD panels on the market are only capable of displaying 8 bit, even if you run an OS and GPU that output 10 bit colour.
And then again certain monitors such as Eizo ColorEdge, NEC MultiSynch and the odd BenQ for example, are capable of displaying 10 bit colour from a 10 bit OS/GPU combo, but only if the monitor-to-system connection has 10 bit capability. This basically means Display Port or HDMI connection.
As photographers we really should be looking to maximise our visual capabilities by viewing the maximum number of colour graduations captured by our cameras. This means operating with the greatest available colour bit depth on a properly calibrated monitor.
Just to reiterate the fundamental difference between 8 bit and 10 bit monitor display pixel depth:
- 8 bit = 256x256x256 = 16,777,216 often quoted as 16.7 million colours.
- 10 bit = 1024x1024x1024 = 1,073,741,824 or 1.07 billion colours.
So 10 bit colour allows us to see exactly 64 times more colour on our display than 8 bit colour. (please note the word ‘see’).
It certainly does NOT add a whole new spectrum of colour to what we see; nor does it ‘add’ anything physical to our files. It’s purely a ‘visual’ improvement that allows us to see MORE of what we ALREADY have.
I’ve made a pound or two from my images over the years and I’ve been happily using 8 bit colour right up until I bought my Eizo the other month, even though my system has been 10 bit capable since I upgraded the graphics card back in August last year.
The main reason for the upgrade with NOT 10 bit capability either, but for the 4Gb of ‘heavy lifting power’ for Photoshop.
But once I splashed the cash on a 10 bit display I of course made instant use of the systems 10 bit capability and all its benefits – of which there’s really only one!
The ability to see 64 times more colour means that I can see 64x more subtle variantions of the same colours I could see before.
With my wildlife images I find very little benefit if I’m honest, but with landscapes – especially sunset and twilight shots – it’s a different story. Sunset and twighlight images have massive graduations of similar hues. Quite often an 8 bit display will not be able to display every colour variant in a graduation and so will replace it with its nearest neighbor that it can display – (putting the 99% Lab pup in the 98% Lab box!).
This leads to a visual ‘banding’ on the display:
The banding in the shot above is greatly exaggerated but you get the idea.
A 10 bit colour display also helps me to soft proof slightly faster for print too, and for the same reason. I can now see much more subtle shifts in proofing when making the same tiny adjustments as I made when using 8 bit. It doesn’t bring me to a different place, but it allows me to get there faster.
For me the switch to 10 bit colour hasn’t really improved my product, but it has increased my productivity.
If you can’t afford a 10 bit display then don’t stress as 8 bit ARGB has served me well for years!
But if you are still needing a new monitor display the PLEASE be careful what you are buying, as some displays are not even true 8 bit.
A good place to research your next monitor (if not taking the Eizo, NEC 10 bit route) is TFT Central
If you select the panel size you fancy and then look at the Colour Depth column you will see the bit depth values for the display.
You should also check the Tech column and only consider H-IPS panel tech.
Beware of 10 bit panels that are listed as 8 bit + FRC, and 8 bit panels listed as 6 bit + FRC.
FRC is the acronym for FRAME RATE CONTROL – also known as Temporal Dithering. In very simple terms FRC involves making the pixels flash different colours at you at a frame rate faster than your eye can see. Therefore you are fooled into seeing what is to all intents and purposes an out ‘n out lie.
It’s a tech that’s okay for gamers and watching movies, but certainly not for any form of colour management or photography workflow.
Do not entertain the idea of anything that isn’t an IPS, H-IPS or other IPS derivative. IPS is the acronym for In Plane Switching technology. This the the type of panel that doesn’t visually change if you move your head when looking at it!
So there we go, that’s been a bit of a ramble hasn’t it, but I hope now that you all understand bit depth and how it relates to a monitors display colour. And let’s not forget that you are all up to speed on Labradoodles!