When you are thinking about the colour space that you want to use to process your images it is a good idea to think about the final destination of finished picture.

Many images are destined to be displayed on the web or printed using an online service or a high street photo lab. For these purposes it is a good idea to supply files in the sRGB colour space. It is possible to supply images to these outlets in other formats but the results do no always display as you might expect.

Most commercial printers require images to be supplied to them in AdobeRGB format even though they will convert them to CMYK. Some agencies, such as Alamy, also specify that files submitted to them are AdobeRGB.

Not all colour spaces are created equal. In an 8 bit file there are 256 values allocated to each of the colours: red, blue and green. Different mixtures of these colours will give all the different colours that can be displayed in an RGB colour space. The range of colour that can be displayed in a colour space is known as its gamut.

sRGB has a relatively small gamut. All of the colours specified in this colour space can be displayed on a standard computer monitor. AdobeRGB has a larger gamut, in other words it can display a wider range of tones, but it can only display the same total number of colours. This means that there is a larger distance between adjacent colours. Most computer monitors cannot display the range of colours present in AdobeRGB.

It might be a good idea to think of this in terms of two ladders, the sLadder and the AdobeLadder. Both ladders have the same number of rungs but the sLadder is shorter and the rungs are closer together. In this analogy, the height of the ladder corresponds to the range of colours that can be displayed and the distance between the rungs corresponds to the distance between the colours.

Of course there are other colour spaces that you could choose. The colour guru, Bruce Fraser is very keen on the ProPhotoRGB colour space. It has a larger gamut than either sRGB or AdobeRGB but maintains fine divisions between colours. Of course there is no chance of displaying the colours of a ProPhotoRGB image on a computer monitor.

So, how do you choose a working colour space? In my view it really depends on the final destination of the image. If it is going to end up in sRGB space, why not edit it in sRGB space. If it is going to end up in AdobeRGB spaced, why not edit it in AdobeRGB space.

The problem comes when the same image my well end up in both colour spaces for different uses. In this case working in sRGB would seem foolish as when the image is converted to AdobeRGB it would still have the gamut of sRGB but with wider divisions between the colours. It would make more sense to work in AdobeRGB and convert to sRGB. In this situation you may end up with unexpected results but it is fairly unlikely. In this situation it may be best solution may be to work in ProPhotoRGB as converting to either AdobeRGB or sRGB should give good results. Understanding ProPhoto RGB from the Luminous landscape is a great article explaining the advantages of this colour space.

One final thing. It is a good idea to start your colour management in-camera, even if shooting RAW. On most cameras it is possible to specify the colour space that you want the image to be in, usually the choice is AdobeRGB or sRGB with other variations of the sRGB colour space. The histogram produced by an AdobeRGB image is different to the histogram from an sRGB image. If you are judging your exposure using the histogram it is a good idea to use the histogram appropriate to your post-processing colour space. So even if shooting RAW, set the appropriate colour space in-camera.

Copyright © Greg Wright 2006 - All rights reserved