Ivan,
The luminance equation comes to mind:
Y = 0.2126 R + 0.7152 G + 0.0722 B
I'm wondering if the Recolor is trying to maintain essentially the same
luminance during the recolor operation. Thus, for example, if you are
shifting to the blue, you might actually want a higher opacity?
Just a guess...
Steve
From: nuke-dev-boun...@support.thefoundry.co.uk
[mailto:nuke-dev-boun...@support.thefoundry.co.uk] On Behalf Of Ivan
Busquets
Sent: Monday, December 16, 2013 12:18 PM
To: Nuke plug-in development discussion
Subject: [Nuke-dev] How is DeepRecolor distributing a target opacity amongst
samples?
Hi,
Not strictly a development question, but I figured there would be a better
chance of someone in this list knowing what's happening under the hood here.
Long story short, I'm trying to implement a procedure to re-target opacity
of each sample in a deep pixel, akin to what's happening in a DeepRecolor
node when "target input alpha" is checked.
I've got this to a point where it's working ok, but I think I might be
missing something, as my results differ from those you'd get in a
DeepRecolor.
My re-targetting algorithm is based on the assumption that the relative
opacity between samples should be preserved, but DeepRecolor clearly uses a
different approach.
Example:
Say you have a deep pixel with 2 samples, and the following opacities:
Samp1 : 0.4
Samp2 : 0.2
The accumulated opacity is 0.52 (Samp1 over Samp2). Note that Samp1
deliberately has an opacity of 2 times Samp2.
Now, let's say we want to re-target those samples to an accumulated opacity
of 0.9.
What I am doing is trying to calculate new opacities for Samp1 and Samp2 in
such a way that Samp1 == 2*Samp2 and Samp1 over Samp2 == 0.9
This gives me the following re-targeted values:
Samp1 : 0.829284
Samp2 : 0.414642
I'm happy with those, but it bugs me that DeepRecolor throws different
results:
Samp1 : 0.798617
Samp2 : 0.503434
Which meets the Samp1 over Samp2 == 0.9 criteria, but does not preserve the
relative opacities of the original samples.
It seems to me like DeepRecolor is applying some sort of non-linear function
to apply a different weight to each of the original samples, but I haven't
been able to figure out the logic of that weighting, or a reason why it's
done that way.
Does anyone have any insight/ideas on what DeepRecolor might be doing
internally?
Or a reason why you might want to distribute the target alpha in a
non-linear way?
Thanks,
Ivan
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