I’m having a issue with fragment blur, and I’m not seeing a very good solution to it. I made fragment blur for g’mic, but alpha images are not calculated correctly hence the adding unnecessary codes. So, other than that, the question is in the title.
As I explained to another user yesterday, G’MIC doesn’t have any concept of the alpha. Opacity is just another channel. I suggest that you try experimenting with the alpha only. You should be getting approximately the same effect without the rest of the image if you are doing it correctly.
I actually may have the answer. What I plan to do is to recursively do the blending mode calculation taking into account of alpha. I can get the alpha channel to be the same as the PDN result, it’s the coloring that bothers me, but recursively calculating should do the trick. blend_alpha 100/n where n is number of images works for 4 color channel image and a empty layer before all of that. For CMYK, recursion would fix the issue.
Here, I achieved it -
Update: Found a code that works for any number of color channels though it assumes the last channel is “alpha”, and ranges are between 0-255
rv / 255 if {s#0!=s#1} v + error "Spectrum numbers must be the same" fi is={s} l[1] s c a[0-{$!-2}] c endl l[0] s c a[0-{$!-2}] c endl repeat 2 l[{$>*2+1}] repeat {$is-2} . done a c endl done f[2] "srcC=i#2;srcA=i#3;dstC=i#0;dstA=i#1;outA=srcA+dstA*(1-srcA);(!outA==0)?(srcC*srcA+dstC*dstA*(1-srcA))/outA:0" f[3] "srcA=i#3;dstA=i#1;srcA+dstA*(1-srcA)" to_gray[3] a[2,3] c k[2] * 255
Now I believe I can really do the fragment blur from pdn with more features and working well on alpha images and with CMYKA images.