Thanks Steve, In this case, I'm talking opacity only.
Color values seem to follow the same logic as non-retargeted recoloring. That is, divide by the input alpha, and multiply by each sample's alpha. It's the re-distributed alpha values that I can't find the secret sauce for :) On Mon, Dec 16, 2013 at 12:29 PM, Steve Booth <st...@boothsoft.com> wrote: > 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 > > > > > > _______________________________________________ > Nuke-dev mailing list > Nuke-dev@support.thefoundry.co.uk, http://forums.thefoundry.co.uk/ > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-dev > >
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