Colour Me Bad

Wel­come to the tra­vails of Colour Man­age­ment? No other words in pho­tog­ra­phy cause so much fear, mys­ti­cism and woe. It’s one of the few areas that has yet to be sim­pli­fied and is still very much a Dark Art. It’s a con­fus­ing quick­sand of tech­nol­ogy, sci­ence and exper­i­men­ta­tion. This arti­cle won’t go over the the­ory, as that would require sev­eral pages of mind bend­ing sci­ence. Instead I’ll give a once over of what are colour spaces and I’ll cover Colour Man­age­ment at a later date. This is not designed to be an tech­ni­cal arti­cle but a very brief intro­duc­tion to the var­i­ous spaces.

Colour mod­els have been around a long, long time with the LAB (Lumi­nance or Lumi­nos­ity, A and B Chan­nels), RGB (Red, Green and Blue Chan­nels) and CMYK (Cyan, Magenta, Yel­low and Key or Black plates). How­ever ICC pro­files (Inter­na­tional Colour Con­sor­tium) on the other hand have been around since 1996 when the sRGB (or Stan­dard RGB) colour space was co-developed by Microsoft and HP. It was cre­ated to sim­plify the dis­play process on a com­puter and it matches the colour space of a con­tem­po­rary CRT display.

Today sRGB is the de facto stan­dard for any dis­play and is endorsed by many of the big play­ers such as Pan­tone, W3C for web usage, and the colour pro­file for SVG web for­mat. The main down­side is its nar­row gamut com­pared to newer for­mats such as Adobe RGB and the ProPhoto colour spaces.

In 1998 Adobe expanded on the colour space due to grow­ing demands of the Pre-Press indus­try. The space is ideal for cre­at­ing and out­putting con­tent to the CMYK colour space and has a very wide gamut which is rep­re­sen­ta­tive of the CMYK process. Many pho­tog­ra­phers use this space as it can closely match the out­put of print­ers (as many print­ers still use the CMYK colour model for printing).

This leaves the third main player in the colour spaces for pho­tog­ra­phers and that’s ProPhoto RGB or ROMM RGB which was cre­ated in 2003. Like Adobe RGB being cre­ated for CMYK out­put ProPhoto was cre­ated by pho­tog­ra­phers for pho­tog­ra­phers. It was cre­ated by the one of the biggest play­ers in the pho­to­graphic indus­try: Kodak. It was designed from the ground up to encap­su­late all vis­i­ble colours that are avail­able on the Ektachrome slides. Due to this it has the largest Gamut of colour that is avail­able to any­one. It also cov­ers over 90% of the LAB colour model. The ProPhoto space has got some caveats as it can cover some colour that doesn’t exist to the human eye and goes beyond both any dis­play and printer capa­bil­ity lead­ing to some severe colour issues. Also con­vert­ing to web can lead to some nasty colour shift­ing and care with some images must be taken.

So that’s the main three colour spaces that are avail­able to you in Adobe Pho­to­shop and Adobe Light­room, the real ques­tion is what should you use? In many ways the argu­ment is very sim­i­lar to the 8bit or the 16bit argu­ment of dig­i­tal edit­ing. Just like a dSLR will cap­ture 12 or 14bits of data when shoot­ing RAW a cam­era will cover a mas­sive Gamut of colour, often far greater than that of sRGB and Adobe RGB. Adobe Cam­era RAW (and other con­vert­ers) will use the ProPhoto (or mod­i­fied vari­ants) space to hold the decom­pressed image before out­putting it to your cho­sen edi­tor or file format.

With this infor­ma­tion we begin to see a pat­tern that tends to point towards the ProPhoto RGB pro­file, and as pho­tog­ra­phers we should always be seek­ing the least lim­it­ing aspect of our work­flow whether it’s using 16bit edit­ing, ProPhoto RGB or some other bound­ary. It comes down to elbow room, if you are going to be doing any kind of colour cor­rec­tion or edit­ing you will want to make sure you don’t hit the bound­aries of your colour space. This can be exhib­ited in small but sig­nif­i­cant issues such as band­ing, pixel cor­rup­tion and it’s more obvi­ous when print­ing large prints such as 12x18” prints or big­ger. The final advan­tage of the large colour space is that you’re less likely to blow a chan­nel result­ing in data loss.

ProPhoto is a large space to work in, and accord­ingly can increase file size. It’s also a ‘work­ing’ colour space and not an out­put colour space there­fore its part of a cal­i­brated work­flow where all the input and out­put sources are cal­i­brated and have ICC pro­files. How­ever few mon­i­tors are capa­ble of dis­play­ing the full gamut of Adobe RGB let alone what’s avail­able in ProPhoto RGB so some­times you are work­ing blind espe­cially on cheap monitors.

I use ProPhoto pri­mar­ily because it gives me the lat­i­tude to do colour cor­rec­tion and edit­ing with­out worry about hit­ting any arti­fi­cial bound­aries cre­ated by the work­ing colour space. It also means when larger gamut print­ers come along I don’t have to worry about re-editing the images. Con­vert­ing to another colour space is rel­a­tively easy once you’ve got­ten use to how an image reacts to alter­na­tive colour spaces.

This is not to say that ProPhoto is always going to be the best space to work in, Adobe RGB is an ideal space for work­ing in if all your are going to do is work with the CMYK colour space, how­ever many newer CMYK+ print­ers far exceeds what this space can encap­su­late. One thought for sure is this argu­ment isn’t going to go away with many pho­tog­ra­phers still using Adobe RGB for colour edit­ing. At the end of the day use the colour space that you’re com­fort­able with using and under­stand it’s limitations.

Fur­ther reading:

O’Reilly Blog Article

Earth­bound Light Article

Lumi­nous Land­scape article

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