2002.03.05 02:20 "16 bit LAB in TIFF - documentation update", by Chris Cox

2002.03.05 20:31 "Re: 16 bit LAB in TIFF - documentation update", by Chris Cox

This is the official update for 16 bit LAB data in TIFF files, part of the documentation update coming out with the Photoshop 7 SDK.

I'm afraid I'm going to abuse your generosity also. But this is a draft, so picking up problems is good, right?

For which encoding?

CIE LAB (PhotometricInterpretation 8):
        -128 => -128
        127 => 127

        256 * -128 => -32766
        256 * 127 => 32512
        (plus some margin)

ICC LAB (PhotometricInterpretation 9):
        -128 + 128 => 0
        127 + 128 => 255

        256 * -128 + 32768 = 0
        256 * 127 + 32768 = 65280
        or
        256 * (-128 + 128) = 0
        256 * (127 + 128) = 65280
        (plus some margin -- identical to the ICC.1:1998-09 encoding)

The math works on my calculator....

That part I didn't change - that came from the original LAB in TIFF notes. It could be optional -- but Adobe and ICC prefer D50, while other software vendors seem to prefer D65.

Chris