At 10:13 AM -0700 9/17/05, christ0pher wrote:
Recently, I have had cause to wonder about the inner-workings of the CMM as it relates to RIP’s.
Of course, I have a basic round-about awareness of what the CMM is - but I’m wondering about the specific functions the CMM is responsible for performing.
Would someone(s) please run a list for me, or give me a link to a related technical paper or reference?
As Mike mentioned (I think) you might want to refer to the Apple ColorSync developer’s guide for ColorSync (www.apple.com/developer). In there is a description of all the things ColorSync does as well as what a CMM does.
The line between the functions of a CMM and of a CMS (color management system, like ColorSync) is a bit blurred.
Basically, the stripped-down function of a CMM is:
create color transformations (called color worlds in ColorSync). This is when you hand the CMM two (or more) profiles and it stitches them together in RAM, readying them for doing transformations. This is where the rendering intent, calculation resolution, etc are set. The creation of a transformation usually involves resampling of the profiles’ LUT data to create a 3D (or n-D) table of transformation numbers. This is very similar to creating a device link profile in RAM.
transform colors - you hand the transformation a list of colors or an image and it converts them from the source space to the destination space. In performing the conversions the CMM finds the closest table entries for each color and then uses interpolation algorithms to calculate its output value. How much oversampling occurs in step 1 and which algorithm is used in this step can affect the quality of the conversion and the amount of time and memory it takes.
some CMM’s (like Adobe’s) add the function of matching black points and scaling the output black point for optimal image contrast (black point compensation).
I think that’s about it in a nut shell. There are probably other functions but that’s the primary use. The CMS adds all sorts of other functions to this including: finding all installed profiles, opening & altering profiles, building of device links, creation of named color profiles, etc.
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
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