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I have a small question about calculating the image rgb value. #327

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Minyeol-Lee opened this issue Sep 1, 2020 · 1 comment

Minyeol-Lee commented Sep 1, 2020

First of all, thank you so much for making such a good library. I'm using it really well.

So..
I'm trying to analyze the heatmap algorithm.
and I have a few questions when drawing heatmap images.

like the image below
i wonder how to calculate the rgb value in this case!

I would be very grateful if you could answer me.
thanks.

helenawang commented Sep 7, 2020

Hi, I'm also curious about how to calculate the colors, especially the overlap part.

After checking the code of heatmap.js and APIs of canvas, I think the calculation of colors is handled by the composite operation of canvas instead of heatmap.js itself, and the details are hidden from us.
However, there are some formulas at standards and https://drafts.fxtf.org/compositing/#simplealphacompositing, which might be helpful to figure out "how to calculate the rgb".

Besides, If you just want to get the exact rgb value of each pixel from the overlap area, perhaps the getImageData API of canvas can help.

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