[Lcms-user] Size of pre and post linearization tables

[John W. <jwe...@pe...>]

We are creating BtoA tables for an output (printer profile):

Input color space: Lab
Output color space: CMYKOVG

   Input Channels = 3
   Output Channels = 7
   CLUT resolution = 33

Total CLUT entries: 33 x 33 x 33 = 35937


When we examine other ICC profiles, they all contain 3 extra tables:

1. 3 x 3  XYZ to XYZ matrix that is normally set to unity matrix
2. Pre-processing matrix for linearizing input Lab values
3. Post-processing matrix for linearizing output ink values

I am completely baffled by the length requirements for tables 2 and 3.

When I examine a profile built with Profile Maker 5 (with multi-channel 
option), it used 514 entries in both tables. Other profiles I have 
checked use 256 entries for these tables.

What are the rules (or rules of thumb) for deciding the length of these 
pre and post processing matrices?

I have checked the ICC4 spec and found no help there.

-- 
John Weissberg
PerfectProof - Accuracy Made Easy