Re: [Openexr-user] CTL questions

[gga]

Florian Kainz wrote:
> Hi Gonzalo,
> 
> The CTL examples that come with playexr and exrdisplay do not make
> use of displayWhiteLuminance and displaySurroundLuminance. (I am not
> enough of an expert to properly model color appearance.)
> 

Okay.  That explains that: not implemented.  So the next question is, is
there any documentation on how those parameters need to be implemented
in a ctl transform?  One of the .ctl 'shaders' mentions an upcoming spec
from AMPAS, but makes no reference to any document.
I imagine displayWhiteLuminance should modify the image's gain somehow,
while displaySurroundLuminance should modify the image's gain/contrast
somehow.  Being that they are measured in candelas per square meter
(nits) I imagine this requires obtaining the proper information from the
monitor's EDID and/or a good calibration device that takes the
environment into account.  I'm still curious how the change in
gain/contrast is to be applied, thou.

> The EXR_DISPLAY_VIDEO_GAMMA environment variable tells playexr and
> exrdisplay the native gamma for your monitor.  

Thanks, Florian.  I'm aware of gamma.  I'm already setting gamma
automatically from the monitor's EDID information if present.

No, basically the issue is due to how transform_RRT.ctl is implemented.
 There's a weird 1D lookup in there that, supposedly, changes contrast
but in my tests really seems to just darken any non HDR image.  Removing
that makes a pass-thru possible.

A final question: what's the status of the licensing (and, more
importantly, the I.P./patent status) of CTL?  The current licensing
reads like a BSD license with a loophole allowing AMPAS to sue anyone
due to patent infringements in California.


-- 
Gonzalo Garramuño
address@hidden

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