Re: [Gegl-developer] [Gimp-developer] unusual (babl/babl/util.h) sRGB tone curve values

On Thu, Aug 23, 2012 at 12:33 AM, Graeme Gill
        it appears that the util.h values are from a draft of the
IEC sRGB standard, not the final one.

Elle Stone wrote:
The standard values are: 0.04045 and 0.0031308.
The util.h values are:   0.03928 and 0.0030402477.

Let's see:

Current IEC specification values:
0.04045 / 12.92               = 0.003130804954
((0.04045 + 0.055)/1.055)^2.4 = 0.003130807229
continuity error of 1 part in 1.3e6

Draft IEC sRGB & util.h values
0.03928 / 12.92               = 0.003040247678
((0.03928 + 0.055)/1.055)^2.4 = 0.003039492412
continuity error of 1 part in 4e3

So the util.h values are a lot less smooth than the sRGB standard values.

Thank you both, I've pushed changes that should make babl adhere to
the current standard.

/Øyvind K.

Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Aug 23 10:26:29 2012 +0200

    Adjust constants used for sRGB gamma

    Spotted by Elle Stone and clarified by Graeme Gill, now updated to
Current IEC
    specification values.

commit 2675787f341ce259f9abec3e326b5efece45ecbf
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Aug 23 10:30:32 2012 +0200

    tests: adjust float to 8bit regression test for new sRGB precision

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