I just read an article elsewhere on the web in which the author proclaimed (in effect) that digital colour management was a waste of time for most people; colour management was for “dweebs”. Sure: if your only interest in photography extends no farther than family vacation snaps printed at your local Price/Costco. If on the other hand you’re reading this article, I suspect that your interest runs a bit deeper, in which case he is decidedly wrong.
So why the controversy?
Why do we even need to talk about “Colour Management”? Can’t our cameras just record colour the way we see it… our monitors display colour the way our cameras saw it, and printers print it the way our cameras recorded it and our monitors displayed it? The short answer is … No!
To begin with, no two devices in the digital photography chain see or reproduce colour in the same way. And yet, we still want the colours we saw (in our mind’s eye, if not with our eyes) to be the colours in our final prints, on our computer screens, or from an offset press if you are shooting for publication. Complicating this is the fact that we all perceive colour in slightly different ways. No two people see a rainbow in precisely the same way. Our colour perception is also influenced by the colour of the illumination falling on , and other colours surrounding an object; the message here is that colour is a slippery subject, one that for a long time defied objective description.
Colour Defined
To come to grips with colour, let alone colour management, what was needed was an objective way of measuring colour. That is to say a way to measure and define colour so that when ever we are talking about say, a particular shade of celadon green, we can all agree on exactly what that particular shade of slightly yellowish green actually looks like.
Work by colour scientists and by the Commission Internationale de l’Eclairage (“CIE” for short, a standard setting body in the world of colour science) produced just such an objective, scientifically based method. As part of this process the CIE defined (among other things) a way to define the limits of human colour perception, again in objective scientific terms. This range of colours matching human visual perception is referred to CIE-XYZ colour space.
So what’s a Colour Space? A colour space simply defines the limits of how a device (including your eyes) sees colour. This is usually defined in terms of a colour’s brightness, hue (where it sits in the range of the spectrum from red through yellow, green to blue, indigo and violet) and saturation (purity). Think of a box of crayons… if the crayons in the box represent the range of possible colours available to you, then it stands to reason that the bigger your box, the more varied colours you can have: in essence the box represents your crayon colour space. Every device has its own colour space. Your digital camera has a colour space that is different from your monitor, which is different from your ink-jet printer, which is different from your local print lab.
Now, before we continue, let’s digress for a moment. In the digital world, for devices like our cameras, monitors, and ink-jet printers, colour is defined in terms of the relative intensity of the three additive primary colours: Red, Green and Blue. Because we are working in the binary math world of digital, there are only a finite number of steps to define the intensity of each primary colour. Currently, most monitors and printers distinguish only 256 discrete levels of intensity (0 to 255) for each colour primary, from black to pure intense colour. Combine all three at maximum intensity, and you have pure white. Combine them in varying amounts and it is possible to define over 16 million different shades. Ok, here’s the rub: the maximum intensity that a particular device can reproduce is always defined as level 255 for that primary colour. Think about that for a moment. If my ink-jet printer can reproduce a maximum intensity red that is brighter and more saturated than that which my computer monitor is capable of reproducing, then if I max out the red on my monitor ie., set it to Red level 255, the red I see from my printer is going to be more intense than that which I saw on my monitor. In colour management terms, the colour space of my printer is different from the colour space of my monitor.
Returning to our topic, we can think of two kinds of colour spaces: device independent, and device dependent. Device dependent colour spaces are those which define how a specific device sees colour. They are those that define the limits of a particular printer paper and ink combination, or of my monitor or digital camera. Device independent colour spaces are those defined in precise colorimetric terms, usually in relation to human colour vision, such as the CIE colour spaces and those derived from it. The value of device independent spaces is that they are useful as a means to objectively relate one device dependent space (such as your monitor) to another device dependent space (such as a particular printer, paper and ink combination). In other words, if we know how a particular device reproduces colour in relation to the CIE space, we can translate this to another device?s colour space. So going back to my earlier example; knowing how my monitor?s max red and my printer?s max red each relate to the CIE space, it?s possible to translate the colours of one to the other in a way that will allow us to match as closely as possible the shade of red we saw on the monitor to the output from the printer. This is in fact what Photoshop and other colour aware applications do, literally on the fly.
So if all this complicated colour translation is necessary, how is it possible to get decent colour from your vacation snaps, with out bothering with good colour management discipline? The answer lies in the fact that virtually all devices such as colour monitors, printers and consumer level digital cameras are designed to, at a minimum, reproduce a limited sub-set of the CIE space known as sRGB. This is a ?safe? colour space, in that few if any consumer level devices can reproduce colours outside of this space. Because of this there is little danger that a colour which can for example, be seen on your sRGB monitor, can not be reproduced on your ink-jet printer, or the local print lab. The colour matching possible in this way is probably in the category of ?not bad? to ?pretty good?. However, current “Pro” and “Pro-sumer” level digital SLR cameras as well as better ink-jet printers such as the Epson K3 ink based units (2400, 3800, etc.) can reproduce colours that lie significantly outside of the sRGB colour space. If you want to get the best colour your equipment is capable of, then you simply have to come to grips with colour management.
In the article I referred to at the outset, the author maintained that everyone should just use sRGB and be done with it. Fine. For many images sRGB isn’t a terrible compromise, but there will be many images you will want to capture that will have colours that lie outside the sRGB colour space. Limiting yourself to sRGB will produce a “safe” image, but also one that could be so much better.
Beyond sRGB
Stepping beyond sRGB takes us into new territory. Out here a colour that we can see on our monitor may not be reproducible by our inkjet printer… or vice versa, let alone by the photo-lab at your local Price/Costco. So out here it becomes really important to know how your particular monitor, and your particular printer/ink/paper reproduces colour. Fortunately getting there isn’t as hard as the “other” author would have you believe. Remember that Windows or the MacOS together with colour aware applications like Photoshop (“PS”) already posses the tools to relate the way one device sees colour to the way in which another device sees colour. All we need to do, is to find a way to tell Photoshop how a particular device sees colour; and that’s where little files called “ICC profiles” come in. These files describe, in a way understood by PS, how the colour capabilities of your monitor or printer relate to the CIE space. Knowing how each relate to this device independent space allows PS to “translate on the fly” so that it can send appropriate instructions to your monitor or printer to produce a desired colour (so long as it is within the ability of that device to do so).
ICC profiles for monitor are created by measuring the response of you monitor using a device called a colorimeter and some associated software. This process is known as profiling your monitor, and is the first and most important step in good colour management. If PS doesn’t know what colour you are looking at, how can it have any hope of telling your printer how to reproduce it?
So what’s the cost of this first and most important step towards good colour management? Assuming you already have a decent monitor? about $US230. That?s the cost of a good hardware colorimeter and associated software from companies like X-rite/Gretag-McBeth or Colorvision. The software in these packages will basically hand-hold you through the entire process of profiling your monitor, create the ICC profile and set your OS to use it correctly. At the risk of seeming repetitious, this is the single most important step in creating a solid colour managed workflow; if you can?t depend on the colours displayed on your monitor, you have no hope of seeing reliable output from your printer. Interesting to note that the other author promotes the use of monitor profiling hardware/software as well… at least we agree on that much.
Photoshop can also work with profiles created to describe how your printer reproduces colour as well. Creating these is considerably more complicated and more expensive. Fortunately paper manufacturers usually provide ICC profiles for a variety of common printers, paired with each of their papers. These are usually more than just good enough, although custom profiles are possible and available from a number of sources that enable you to wring the best possible colour performance from your printer.
Colour management is not just for people obsessed with technological minutiae. Very real improvements in the extent and accuracy of colours in your prints are possible with relatively modest investments in time and money. Once set up, the colour management process is virtually transparent to the user. It?s a well worth while endeavour in my book.
I?ll go over setting up Photoshop for colour management and discuss RGB editing spaces in a later article.