[Cin] Again on plugins in floating point (HDR)

Andrew Randrianasulu randrianasulu at gmail.com
Fri Dec 1 18:11:58 CET 2023

пт, 1 дек. 2023 г., 18:59 Andrea paz via Cin <cin at lists.cinelerra-gg.org>:

> I tried to make other changes to the plugins for Color Correction to
> be able to make it also see out-of-range (HDR) values and be able to
> change them. All of this involves floating point calculation. I tried
> changing the range of the following plugins:
> Alpha; Color3Way; ColorBalance; Gradient; Histogram Bezier e Overlay.
> If interested, I can report attempts to modify the code, but I got
> good results only with Color3Way.
> More in detail:
> Alpha: My modifications ruin the plugin. Probably widening the range 0
> - 1.0 leads the algorithms to wrong results. However, I think the
> original plugin works in floating point.
> ColorBalance: From my tests I did not notice any difference with the
> unmodified plugin (I used an appimage). I am under the impression that
> this plugin already works in floating point and does not need
> modification.
> Gradient: Here again I find no difference with the original plugin.
> Again, I have the impression that the plugin already works in floating
> point.
> Overlay (shared effect): I don't notice any difference with the original
> plugin.
> Histogram Bezier: I tried extending the range similarly to Histogram
> (which works well in HDR, after modification). In this case I see no
> change. The code is much more complex and it is probably not enough to
> delete the CLAMP.
> The change I made is to the file "bistogram.C"
> line 361 I changed the value of 1.0 to 10.0.
> I also tried editing the file bistogramconfig.C
> line 110 e 111 I changed the value of 1.0 to 10.0.
> line 229 I changed the value of 1 to 10.
> I put these details because the plugin is very important for CC and I
> would love it if someone more experienced than me could make it work
> on out-of-range data as well. Besides, the plugin is not only a
> histogram but also uses the very important "Curves".
> For the Videoscope plugin I could not make changes because the code is
> too complicated for my skills; similarly to Histogram Bezier.
> Finally I describe Color3Way, in which the modification worked. In the
> original plugin the color wheels already seems to work in floating
> point, but not the V bar of brightness values (which are clipped).
> With the modification the V bar also works on out-of-range data.
> The modification is as follows:
> File "color3way.C":
> line 281 I changed the value of 1.0 to 100.0.
> line 284 I changed the value of 1.0 to 100.0
> (I have also tried other values, e.g., 10.0, and the clamp always
> works up to those values).
> The floating point calculation works for both the saturation bar and the V
> bar.
> With the tests done so far, I have had no problems or errors/warnings
> on the terminal.
> I did the tests with exr images and then enabled the internal CinGG
> engine (but in the tests it also works with "ffmpeg first"). I set the
> color model to RGBA-FLOAT (inescapable: with integer 8-bit models you
> cannot have HDR) and the color range to 2020 NCL (but it works with
> all possible settings, not relevant). The graphics driver is X11
> because with X11-OpenGL it does not work.
> Used patches:
> 0001-TEST-Simpler-unlimited-float-overlay.patch
> 0002-Allow-negative-numbers-in-overlayer.patch
> noclamp_in_histogram.diff
> Manual changes in color3way.C
> I am happy with the success with Color3Way (as with Histogram) because
> I believe it will become increasingly important to work on HDR video
> in the future. On the other hand, I regret not having success with
> Curves (Histogram Bezier) because it is an essential plugin for CC.

Thanks for experiments!

I wonder if anyone who worked on colour correction plugins in cinelerra
still can be contacted? I do not feel very comfortable in this area,
because some advanced usage of plugins/modes/rerouting already bite us
earlier ....

> Cin mailing list
> Cin at lists.cinelerra-gg.org
> https://lists.cinelerra-gg.org/mailman/listinfo/cin
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