Show the brightness channel for each pixel

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Thanks for your reply.

I can split the channels, but later I don't know how to make that vectorized operation. Looping is too slow.

I want to have blue or red, and discard green. I uploaded an image of the result, maybe there is another way to achieve the same.

to make that vectorized operation

what ? try to be more concise. what do you want to do with it ?

Thanks, I didn't know I could, I tried to add them before by replying my own question.

thanks for the edit, btw !

By vectorized operation I mean operations that are applied to whole arrays instead of individual elements, just like numpy in Python

if the 2nd image is the answer to your question, then i don't understand it.

The second one is made by WebGl, which uses the GPU. I wonder if CV has implemented a function that allows this operation natively.

but it's not at all showing "the brightness channel"

Yes, I know, for the brightness I could do (r,0,0,255) instead of (255, 0,0, 255). My application doesn't require that information.

I can do it with a loop in CV.Mat.data, but that kills the performance to ~1fps