Re: [Gimp-developer] Exposure clamping.

[Øyvind Kolås <pippin gimp org>]

On Tue, Nov 7, 2017 at 7:46 PM, Mario Sottile - Marionetas Mey
<mariomey gmail com> wrote:
> I created a 32bits floating point, lineal light Gamma, new archive. I select
> 50% RGB gray color and fill everything. I applied a Exposure of 10 to it.
>
> Now, I took the color picker and click on image. It says:
>
> If 0.21 is the middle gray for lineal middle gray of sRGB...
>
> 2^10= 1024
> 1024*0.21= *215*
>
> ... but GIMP says: 21,4.
>
> Why is it clamped at +- 6.7 stops?

Thank you for spotting this, the exposure operation encoded a maximum
gain of 100.0 when avoiding a division by zero, this arbitrary limit
has been increased in git master:

commit a1c2b693e92c07c3af8b6a632fe5228422d23f3b
Author: Øyvind Kolås <pippin gimp org>
Date:   Wed Nov 15 01:39:13 2017 +0100

    exposure: adjust clamping to avoid division by 0

    The code contained MIN (reciprocal, 0.01) to avoid division by
zero, resulting
    in a maximum gain of 100.0, this changes it to a maximum gain of 1000000.0,
    with some non-photographic sources such gains are entirely reasonable.


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