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What working space to use
There are a wide range of colours (and brightnesses) that can be seen and measured.
One way to represent these was defined a while ago as an international standard by the CIE.
For various practical reasons, digital images are often created, worked on and printed in subsets of this standard.
These are known as colour spaces. The definition of any space represents the range of colours (and brightnesses) it encompasses. This is also known as the gamut of the colour space.
Smaller colour spaces such as sRGB might hold some 35% of the full CIE range, whilst larger ones such as Adobe98 (aka A98) contain around 50%. There are even larger spaces such as ProPhoto that you will hear of.
The question most people ask when they learn this difference between spaces is 'why not just use the biggest'.
It turns out that there are trade-offs between using them and the choices are not as clear cut as you might first think.
I'll show a few examples and later give my reasons for my own choices, however I'd encourage you to experiment with some of your own images to get a feel for what is right for you.
First of all, a 'simple' case - images on the web.
This is the easy one - there is very little colour management on the web. I wrote an article a while ago about Colour Management and the Web, and I'm sad to say not a great deal has changed.
Essentially, when producing photos for the web, you might as well work in sRGB. All the images for this article were converted to sRGB, to give the best chance that the most people could see the points I'm illustrating.
Image use on the web is a compromise - I could have produced the entire article with images in Adobe98 (or even ProPhoto), but then only people using Safari, or FireFox with colour management enabled would have seen the image anything like I intended.
If you also assume that the majority of people also have not calibrated their monitors, then I can safely say I've no idea what these pictures look like on -your- screen. I'll just use sRGB and hope for the best.
I've heard several people say that for 'real world' images, there is not much that sRGB loses out on.
Well, for an example, lets take the trees image.
The screen grab below (converted from monitor space to sRGB for web use) shows the trees viewed in three different colour spaces.
From left to right we have ProPhoto, Adobe98 (A98) and sRGB.
I've just duplicated the image twice after opening it.
Next I've used a Custom Proof for two of the windows, selecting A98 and sRGB. This shows what they look like in those colour spaces.
The custom option will show all the profiles on your computer, and allow you to select one.
Don't worry about other settings at the moment.
You'll not see much difference in the images below (given the convoluted paths that the images are taking from my screen to yours, that's hardly surprising).
Move your mouse over the image to see the Photoshop gamut warning applied.
It's normally grey, but I've altered it to bright red in the preferences, so as to show it here.
All the pixels that are of a colour that doesn't fit in the colour space are turned red.
I've zoomed in to show a bit more detail below.
As before, move your mouse over the image to see which pixels don't fit.
So much for real world images fitting into sRGB...
As I've mentioned several times (and will again), you are not seeing what I'm seeing.
Few monitors can display the whole A98 space, and none can manage a huge space like ProPhoto.
Your image is being fitted into what can be displayed by your monitor. This process uses the monitor profile for your display.
Just like any other profile you can select this for soft proofing and see what pixels are beyond the gamut of your monitor.
Move your mouse pointer over the image below to see how much of this photo is beyond the gamut of my monitor.
Lots of red pixels, but not as many as when proofed against sRGB
This does mean that when editing an image, you are just seeing pixels at the best colour your particular monitor can manage. This is potentially an issue when you are editing images in a larger colour space.
- Do remember that the Adobe gamut warning doesn't show how much out of gamut the colours are, only that they are. The point I'm trying to make here is that they exist - whether this matters and what you might do about it are different matters alltogether...
As I've mentioned, if you are just outputing images for web use, then there is little need to be concerned with colour spaces and profiles - just use sRGB.
However printers also have colour spaces. A printer icc profile contains a definition of the output colour space of the particular printer/ink/paper combination it was created for.
The two examples below show the range of colours that two different papers can manage when printed on my Epson 7880.
Neither look terribly good in this particular example.
- Proof with absolute colorimetric rendering intent to see this degree of difference. Other intents map colours from one space to another, so in effect, there are no out of gamut colours.
Fortunately when printing, colours can (automatically) be mapped to what the printer can manage, through choice of rendering intents (see the refs. for more on this).
It's noticeably worse if you look at the range of colours available from a Fuji Frontier (a typical printer used by many photo labs).
- With this mapping (rendering intents) and good printer profiling, a print can still look very good even if quite a lot of colours can't be reached. Fortunately, our visual system is very good at using relative appearances rather than absolutes.
I'm not going into the detail of matching 3D representations of colour spaces here, but it's a good approximation to say that if you print on a high end inkjet printer (with good paper and icc profiles) then the gamut available comfortably exceeds the range of sRGB in a number of areas. If you print via a lab using the likes of the Fuji Frontier, then it largely fits within sRGB.
Hopefully the images above show some of the variations between different spaces.
For Web use I use sRGB as the 'best bet' that you will see my images as I intended them.
On the web, there is another reason for picking sRGB, and that is that you are often using 8 bit images such as JPEGs. 8 bit images have a limited range of colour values. If you spread these out evenly in a smaller space such as sRGB then the values are closer together than in a larger space. The colours are represented more evenly and less prone to banding or other artefacts.
For images I want to print though, I'm working at 16 bit, where there are more than enough colours to go round.
If I was printing via a lab, then popular wisdom suggests I'd have little to gain by using A98 over sRGB, although a more detailed analysis of profiles shows that some yellows that a Fuji Frontier can manage, are beyond the sRGB range.
However I don't use this sort of printer for my prints.
I build my own printer profiles and choose papers that show the benefits of the pigment inks in my printer.
Choosing between A98 and sRGB is no contest for my own print applications. A98 has visibly larger ranges in many colours.
In fact, Adobe created A98 specifically to better match the range of colour available in CMYK printing.
In prints, this shows in richer cyan to green midtones, yellow to magenta highlights, and green shadows. All quite useful for landscapes for example.
For good quality printing (working at 16 bit) then it's Adobe 1998 every time for me. For web and 8 bit working it's sRGB.
Or is it?
I can take JPEGs with my camera and have a choice of colour spaces. If I set the camera to A98 then I'm capturing a wider range of colours. If I'm not editing the images much and printing via a Lab, I might well choose A98 just to get that bit more out of my prints - then again, I virtually never use JPEGs out of the camera and don't get prints made by anyone else.
The image shows a representation of the sRGB colour space (solid shape) overlapping the space (wire frame) representing an icc profile for Fuji Crystal Archive Luster Surface paper at one particular lab.
Move your mouse over the image to see the expanded range of A98 and notice how it covers much of the clipped area that is missed by the sRGB space.
Photo machines at labs are much more variable than a good inkjet printer.
If you want top quality printing then look for a lab that offers a range of colour management advice for customers. If you want cheap prints at the local supermarket then just stick to sRGB.
- Note - A health warning for when you see diagrams like this in reviews and articles. It is very easy to mis-read what you see and attach a lot more significance to slight overlaps or clipping. Without detailed explanations of what is being shown, take such information as a visual aid, no more. Graphs and assorted plots are sometimes found in articles just to fill space and make them look interesting. Some reviews of papers for printing seem to be particularly rich in accurate but meaningless data.
Even bigger colour spaces
In the original aspen tree examples at the top of the page, the image at the left is in the large ProPhoto colour space. This is a huge colour space that expands beyond the visible range in some areas, to allow colours that just aren't 'real' and can't be reproduced at all.
- Unreal colours? Think of 'minus two oranges'. This has meaning, as in 'six oranges minus two oranges' but there is no such thing you can point to as 'minus two oranges'.
Using a huge space like this means that you can now retain the full range of colours that your camera is capable of recording (a colour space in itself).
I've seen a lot of debate as to whether using a space like ProPhoto is any use in 'the real world'. There are a some colour images I've taken for prints that include small areas beyond A98. Many are perfectly fine in A98.
Whilst the use of A98 over sRGB is an easy choice if you do your own printing, the choice of ProPhoto is less clear.
For my commercial work, I supply much of it in sRGB - this is 'safer' with a lot of clients.
Some clients (brochures and annual reports for example) prefer A98 for the better dark greens amongst other things.
No-one (as yet) has asked for a larger space.
For a current series of colour prints (the Gallery will be updated eventually) I'm doing my raw conversions into ProPhoto. The gamut warnings suggest that there are areas that will be improved, but as yet I can't honestly say I can see much difference in prints (this using our PDV3 print viewing stand). However, I'm not losing anything in doing this, as far as I can see.
I often get asked for suggestions about learning more about the nuts and bolts of Colour Management.
My usual suggestion is Bruce Fraser's Real World Colour Management. My own copy is well thumbed. It's my first port of call if I'm asked a question and I feel I don't quite understand an issue well enough to be absolutely sure of an answer.
Check latest price/availability from Amazon.com or Amazon.co.ukRWCM 1st Edition RWCM
RWCM 2nd Edition RWCM
See some other books Keith has on the shelf, on our Books Page
So, for brightly coloured images I'm sticking to ProPhoto for some colour prints I'm printing myself.
I work in A98 for much of my commercial photography, even though the majority of files I supply are in sRGB.
I should add that if you start with an image in a small space like sRGB, there is usually not much to be gained from editing in a larger space, particularly if it's an 8 bit image like a JPEG.
One last area, where I do regularly use ProPhoto, is black and white. Or more precisely, I use it for producing the colour images that I then turn into black and white.
If a colour space captures finer gradations in colour, then those gradations can be used to potentially bring out greyscale texture upon conversion, particularly using more complex conversion techniques such as Nik Silver Efex.
So, you're saying...
Understand the differences, experiment with some of your own images and decide which factors actually matter to you. I generally take the approach that the more strident and forthright opinions you read on the web, the more you should challenge them.
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It's also worth noting that most people couldn't spot many of the differences unless they had direct comparisons under specially set up lighting ...and had it pointed out to them.
If you are of a perfectionist nature, then realise that at a certain point it's actually far more productive to go out and take more photos, than to worry about about minutiae. I'm not someone who paints behind my radiators (if it can't be seen then I'm not that bothered) realising (IMHO) that perfection is often the enemy of excellence ;-)
Keith is always happy to discuss matters raised in his articles. You can Email Us
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