[argyllcms] Pre-linearization table for BtoA LUT
- From: John Weissberg <jw@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 18 Oct 2007 13:54:28 +0200
When I build profiles with Argyll using the tags:
-bh -ni,
then the BtoA tables have a pre-linearization table containing 2048
lines and a LUT that is 33 x 33 x 33.
As I understand it, the real purpose of this pre-linearization table is
to guarantee that the value for a or b corresponding to the case where
the index in the 33x33x33 matrix is 16 actually map to a or b values
very close to 0.
I am still a bit confused as to how this pre-linearization matrix works.
Below are the values for L,a,b that correspond to the 33x33x33 matrix
indices prior to processing with the pre-linearization:
idx L a b
0 0.00 -128.00 -128.00
1 3.13 -120.03 -120.03
2 6.25 -112.06 -112.06
3 9.38 -104.09 -104.09
4 12.50 -96.13 -96.13
5 15.63 -88.16 -88.16
6 18.75 -80.19 -80.19
7 21.88 -72.22 -72.22
8 25.00 -64.25 -64.25
9 28.13 -56.28 -56.28
10 31.25 -48.31 -48.31
11 34.38 -40.34 -40.34
12 37.50 -32.38 -32.38
13 40.63 -24.41 -24.41
14 43.75 -16.44 -16.44
15 46.88 -8.47 -8.47
16 50.00 -0.50 -0.50
17 53.13 7.47 7.47
18 56.25 15.44 15.44
19 59.38 23.41 23.41
20 62.50 31.38 31.38
21 65.63 39.34 39.34
22 68.75 47.31 47.31
23 71.88 55.28 55.28
24 75.00 63.25 63.25
25 78.13 71.22 71.22
26 81.25 79.19 79.19
27 84.38 87.16 87.16
28 87.50 95.13 95.13
29 90.63 103.09 103.09
30 93.75 111.06 111.06
31 96.88 119.03 119.03
32 100.00 127.00 127.00
I would love if someone would help me understand exactly the formula
used to apply the pre-linearization table to these points.
Attached is an excel file containing the 2048 points for the
pre-linearization table from my profiles.
--
John Weissberg
PerfectProof - Accuracy Made Easy
www.perfectproof.com
www.printers-website.com
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pakready.perfectproof.com
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