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Exposure clamping.

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Exposure clamping. Mario Sottile - Marionetas Mey 07 Nov 18:46
  Exposure clamping. Øyvind Kolås 15 Nov 00:48
   Exposure clamping. Mario Sottile - Marionetas Mey 16 Nov 12:09
Mario Sottile - Marionetas Mey
2017-11-07 18:46:03 UTC (about 7 years ago)

Exposure clamping.

Hello there. I made a simple test in Gimp 2.9.6 commit c97c2fe06d.

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?

What if I want to edit an EXR from Blender?

Thanks in advance.

Marionetas Mey

Mario Sottile - Director
(011) 15.6283.1576
www.mariomey.com.ar
info@mariomey.com.ar
Øyvind Kolås
2017-11-15 00:48:39 UTC (about 7 years ago)

Exposure clamping.

On Tue, Nov 7, 2017 at 7:46 PM, Mario Sottile - Marionetas Mey 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
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.

/pippin - http://pippin.gimp.org/

Mario Sottile - Marionetas Mey
2017-11-16 12:09:18 UTC (about 7 years ago)

Exposure clamping.

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:

Thanks, man! It will be very usefull for, as you said, non-photographic sources.