Do you dream in color? After the two weeks of my "spare" time spent writing a ICM color profile editing program I dream in color a lot.

There are rubix cubes on steroids with letters L A B on the sides.

And some with RGB and others XYZ.

Seriously now what is this craziness about � it is about making my printer print colors I like when using a third party archival ink.

If you are new to this I have some bad news.

1. Not all perceivable colors can be displayed on a computer.

2. Not all the colors which can be displayed on a computer can be printed on a color printer.

3. Not all colors which can be printed on a dye based printer can be printed on a pigment based (inkjet) printer.

4. Different combinations of types of ink and paper produce radically different colors with identical printer settings.

We can't do much about the first three points but we can try to manage the available colors set to produce nice prints.

Now before I get into the nitty gritty I'm going to have a little whine and I'm sure I'm not alone here.

I want to whine about three things

1. I think the average consumer is not informed about total cost of ownership of printers.

2. Users are ripped of buying ink cartridges and at least one manufacture (epson) tries to prevent users from using 3'rd party ink by chipping their cartridges.

3. Users are rarely informed what sort of life they can expect out of their prints.

The sad thing is espon make really good printers - but unless they stop this non-sense my next printer will probably be a canon.
My personal example is I bought an epson stylus 760. It produces amazing results but the price of ink cartridges is outrageous and refilling doesn't work too well at all. And to top it off the 3'rd party ink refills I used have an extremely short life if exposed to light (and fumes?). My anwser to all this was to build a CIS (continuous inking system) and buying an archival ink set � (generations-2 from media-street). I built the CIS because the price quoted for a commercial system was ridiculous. You can see my CIS in the photography area of my home page (I won't link it because it may move). Unfortunately the new ink set make terrible looking prints with weak cold yellow and reds. It isn't just a matter of adding more yellow because that wrecks the other colors. You need to adjust some parts of the pallet one way and others differently. This is something ICM color management can do. Custom ICM profiles can be bought and if your luck you might find a free profile close enough for your needs (I didn't). Software to create profile can be bought but I have no idea how good they are. I am not aware of any free-ware apart from mine.

Being a hacker (not cracker) type with the motto "They're only numbers � how hard can it be" - I dived in to writing my own.

If you at all serious about this you need to look at http://www.color.org/ where you can find the specs for the ICM files. There is also some handy stuff athttp://www.littlecms.com/. At http://www.logicol.net/color_calc.html you can find a color space calculator and code examples to swap between color spaces.

I won't explain ICM in any great detail but the gist is to have a universal way for programs to communicate color information and this is not RGB and a way to translate the colors. The common or PCS (profile connected space) is usually CIE LAB. The profile usually contain a number of CLUTs (color look up tables) but my program only deals with two with the main aim of modifying one of them. This CLUT is called B2A0 (or BtoA0) it has the data for converting from PCS to the device � ie the printer. There can be multiple B2A cluts but I ignore them. I can also look at the A2B CLUT but this is mainly educational. In the beginning I thought the A2B clut may be used to convert the input to PCS but this does not appear to be the case.
Each CLUT has a 3*3 matrix, several lookup tables, the for LAB the matrix does nothing and the input and output table are usually straight line functions which also do nothing. That leaves the CLUT work horse which is a three dimensional lookup table (I'm only talking about 3 channel (RGB) conversion, more channels could mean more dimensions) . In an our case the A2B table the 3D CLUT the cells (elements) are addressed using R, G and B and the cells contain three values L, A and B. The B2A 3D CLUT is the other way around - the cells are addressed using L, A and B and the cells contain RGB values. The tables don't contain all possible colors so the ICM software interpolates.