[argyllcms] Re: Pre-linearization table for BtoA LUT

John Weissberg wrote:
Thanks very much for you explanation. I am sorry to be a bit thicker than the average. Since our BtoA tables are 16-bit with V2.2 profiles, I understand that the mapping below (for 8-bit profiles) is not correct: 



idx    L    a    b
0    0.00    -128.00    -128.00
1    3.13    -120.03    -120.03




30    93.75    111.06    111.06
31    96.88    119.03    119.03
32    100.00    127.00    127.00
Would it be too much trouble to ask you what the correct mapping is for a 16-bit LUT? 

Simply divide the V2 16 bit range into the resolution of your CLUT.
The V2 16 bit range is listed in table 32 & 33 starting on page 43 of
the V4.2 spec:

Idx     L*              a*              b*
0       0.0000          -128.0000       -128.0000
1       3.1372          -120.0001       -120.0001
2       6.2744          -112.0002       -112.0002
3       9.4116          -104.0004       -104.0004
4       12.5488         -96.0005        -96.0005
5       15.6860         -88.0006        -88.0006
6       18.8232         -80.0007        -80.0007
7       21.9604         -72.0009        -72.0009
8       25.0977         -64.0010        -64.0010
9       28.2349         -56.0011        -56.0011
10      31.3721         -48.0012        -48.0012
11      34.5093         -40.0013        -40.0013
12      37.6465         -32.0015        -32.0015
13      40.7837         -24.0016        -24.0016
14      43.9209         -16.0017        -16.0017
15      47.0581         -8.0018         -8.0018
16      50.1953         -0.0020         -0.0020
17      53.3325         7.9979          7.9979
18      56.4697         15.9978         15.9978
19      59.6069         23.9977         23.9977
20      62.7441         31.9976         31.9976
21      65.8813         39.9974         39.9974
22      69.0186         47.9973         47.9973
23      72.1558         55.9972         55.9972
24      75.2930         63.9971         63.9971
25      78.4302         71.9969         71.9969
26      81.5674         79.9968         79.9968
27      84.7046         87.9967         87.9967
28      87.8418         95.9966         95.9966
29      90.9790         103.9965        103.9965
30      94.1162         111.9963        111.9963
31      97.2534         119.9962        119.9962
32      100.3906        127.9961        127.9961

Graeme Gill.

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