count transparent pixels in a layer

[Lukasz26371223zhpe]

Hi,

I have a foreground render video (which has an alpha so we know what pixels are transparent vs not).
And I lay it on top of a background video. Basically what i want is to be able to count the pixels that
are transparent. And separately the ones that are not.

Is there an easy way to do it ? can be done manually ? or using scripting ? or maybe i should write a plugin using the SDK for it (e.g. an effect plugin that would be applied to a layer) ?

I'm new to Adobe PP and video editting, but i hope the terminology i've used is OK. If anything unclear, do let me know.

Thanks,
Lukasz

[Bruce Bullis · Accepted solution]

You understand it correctly; an AE API effect plug-in, running in PPro, would be able to detect the alpha (opacity) value of each pixel. 

I'm curious; what would you do, with that information? "At this moment in time, there were 17,239 transparent pixels in the source layer"...?

[Lukasz26371223zhpe]

Thanks for the answer.

I want to do that to capture the information about the ratio - number of transparent pixels vs number of all pixels. Cause that render video has an embedded object and i'd like to know its relative size. Hope that makes sense.

So the correct approach would be to write a plugin that has access to the pixels and counts the ones with alpha value zero or close to zero. So AE SDK is the right tool for the job and there's no easier alternative, right ?

[Bruce Bullis]

Yes, AE effect API (as explained in the AE C++ SDK) is the right approach.

You're placing a lot of trust in the Editor to not any of a million different things, that could impact the alpha value of those pixels. 🙂