[argyllcms] Scaled Rec709 TRC question

  • From: János, Tóth F. <janos666@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 11 Feb 2011 13:19:42 +0100

I am currently working on a MPC-HC patch which tries to improve the quality
and give more control to the user over the CMS settings.

Some people believe that a custom scaled Inverse-Rec709-Encode curve is
better for viewing Rec709 materials than the good-old pure-power curves.

There are three existing "Ambient Light" options: Bright, Dim, Dark and they
currently represents pure-power TRCs wit gamma: 2.2, 2.35, 2.4
I don't want to change that. But I want to add three differently scaled
Rec709 curves beside the currently available pure-power curves.

The users who like the scaled curve (for example cyberbeing from
forum.doom9.org) says I should try to simulate the ArgyllCMS/dispcal

MPC-HC works with lcms2.1 and I don't want to change that either (at least
for now). So, I want to ask for three parameter sets to construct "Type 4"
tone curves with lcms.

I think this is the exact inverse encode curve:

exponent = 2.2;
coefficient_exponential = 1/1.099;
constant = 0.099;
coefficient_linear = 1/4.5;
  constant_linear_range_length = 0.018;

But it looks very bad on the screen and I am not sure how to change them to
match with ArgyllCMS/dispcal. (My short "trial and error" caused errors

Here is the current test buid:
(Right click on the middle, Renderer settings, Color Management)

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