The Color of Toast
A lot has been written about color management as it has evolved over the years. Some of it is good and some of it is not so good. Some color management information is conveyed via thick books with a lot of mathematical equations in them. But for those out there that are not color scientists, there is one article that I think best describes what color management is, and how it's used in a very simple to understand way.
A number of years ago, Steve Upton, president of Chromix and the brains behind ColorThink - the indispensable color management software tool for evaluating ICC profiles and color workflows, wrote an excellent article called "The Color of Toast". This article has been around for quite a while, but is still very relevant. It uses a simple, brilliant analogy that makes color management concepts easy to digest, with or without strawberry jam.
The Color of Toast...
Let's say you get up in the morning, walk out to your kitchen and place a piece of bread in your toaster setting it to a level of "4". After a little while a certain color of toast pops out - hopefully a pleasing color. Now if you take the next piece of bread in the loaf over to your neighbors and put it in his toaster at the same setting of "4" do you think you will get the same color of toast?
This is the problem of color management. The settings used on the toaster do not necessarily produce the same colors. As in the toaster, RGB and CMYK values on your computer are also just settings. And, just like the toasters, when they are sent to different devices, they produce different colors!
Now if you were a severe toast geek, you would toast 10 pieces of bread in your toaster; one at every setting. Then you would lay them all out in order on your kitchen table, grab the bag of bread and head over to your neighbor's. Avoiding his bewildered stares you would toast 10 pieces of bread in his toaster and take them back to lay on your table beside your toaster's work. Fanning through your Pantone independent toast guide, you would decide that "B" was, in fact, the color of toast you prefer. Looking up and down your toaster column you would confirm that yes, indeed, "4" is the setting on your toaster that will get you the color you want - you know this after several mornings of frantically waving smoke away from the alarm on your kitchen ceiling. After looking over your neighbor's toaster column, you note that a setting of "6" is what is needed to get the color you want from his toaster.
This, in essence, is what color management is all about. Carefully sampling what a device (monitor, printer, toaster, whatever) will do and then comparing it to an independent guide for actual color. In the case of the toast we used the fictitious Toast Guide and in the case of computers we typically use the Lab color space. Lab is a whole 3D range of numbers across 3 coordinates (L for lightness and a & b for color information). The important thing about Lab is that it is actually COLOR. That is, a number that represents a sensation.
To get the same color from different toasters, we needed to sample all the colors of toast the lowly machine could produce and then compare them to an independent guide. This lookup table is the equivalent of an ICC profile.
To get the same color from different devices - what we are basically trying to do here - we need to sample all the colors that device can produce and setup a table that converts between the device settings - say, a monitor - and the colors it produces at those settings. For a monitor we attach a device to the monitor and then run software that walks through a list of settings,: red (255,0,0), yellow (255,255,0), green (0,255,0), and so forth. At each RGB value, it takes a reading with the instrument and gets a Lab color back. After running through a long list that only a computer should have to suffer, a profile is built for that monitor.
If we want to get the same color from our printer as well then we also need to build a profile for it. The same technique applies. We send a file out to the printer that contains a long list of settings - for example: cyan (100,0,0,0), blue (100,100,0,0), magenta (0,100,0,0), and so forth. We then read each patch on the paper with a device like the Eye-One that supplies Lab values for each corresponding set of CMYK settings that were sent. A few calculations and your computer produces a profile for your printer. Great, you think, but how do I use these things? That depends on what you are trying to achieve.
A good example is when you want to get the file you print to match the one you see on screen. The file on screen is, by definition, in MonitorRGB and you need to convert it to PrinterCMYK. If you apply the monitor profile to the file, it will convert all those MonitorRGB settings which are unique to your monitor to Lab (remember the toaster).
Lab, you will recall, is color - so we are out of the arbitrary world of settings that only work for your monitor and on to something much more useful.
Any profile can be applied to those Lab values to get the color you want. In this case, we want the color to go to your printer. When the printer profile is applied it formulates the correct CMYK settings for each color in your file. A good quality profile will do a great job of matching those colors within the abilities of the printer.