Chaining GPUImageChromaKeyBlendFilter
Wed, 08/01/2012 - 08:17
I started playing around with GPUImage yesterday and I am impressed. I was up using it in matter of minutes, but today I have been struggling with chaining the GPUImageChromaKeyBlendFilter filter.
currently I am doing something similar to.
[chroma1 addTarget:chroma2];
[foreground addTarget:chroma1];
[foreground processImage];
[background addTarget:chroma1];
[background processImage];
return [chroma1 imageFromCurrentlyProcessedOutput];
For one filter (only having chroma1) this technique is working but not for 2 or more.
Any ideas is much apprechiated.
Wed, 08/01/2012 - 10:39
#2
Try reordering it to this:
[foreground addTarget:chroma1]; [foreground addTarget:chroma2]; [background addTarget:chroma1]; [background addTarget:chroma2]; [foreground processImage]; [background processImage];
Under the new way that I've configured the blends, this should ripple down the filter chain appropriately.
Wed, 08/01/2012 - 18:14
#3
Thanks that seems to work fine and is much faster.
Another related question. It seems like the thresholdSensitivity setting responds quite differently to different colors. Red requires a very low threshold to be replaces whereas blue and green seem to be quite hard to replace and need a higher threshold.
This seems a bit odd to me, but maybe I am doing something wrong.
Wed, 08/01/2012 - 18:48
#4
The color "distances" are based on Y, Cb, and Cr, and are based on a distance algorithm proposed by Apple in one of their samples. You can look at the fragment shader code to see how I calculate this. There might be a better way to calculate this, but that's what I'm using right now.
I finally got it working by doing the following:
[foreground addTarget:chroma1];
[foreground addTarget:chroma2];
[foreground processImage];
[background addTarget:chroma1];
[background processImage];
[foreground processImage];
[background addTarget:chroma2];
[background processImage];
return[chroma1 imageFromCurrentlyProcessedOutput];
Seems a bit wasteful to run processimage twice on each image. Am I doing things backwards? Is there a more effective way to do this?
(I see a pretty harsh slowdown for each new chroma filter I add).