Legacy ImageMagick Discussions Archive

IM 6.7.6.7 Q16 Mac OSX Snow Leopard

I could be wrong here. But I was under the impression that IM has for some time now, when using -channel a -separate, gives the transparency channel. But it seems to be giving the opacity channel. Was this not switched a while ago? Or am I mis-remembering?



convert alpha3.png -channel a -separate alpha3_alpha.png




convert alpha3.png -background skyblue -flatten alpha3_blue.png




convert alpha3_blue.png -channel a -separate alpha_blue_alpha.png



The above is extracting the opacity and not the transparency. Did you not switch this so that we get the transparency? Or is that only to come in IM 7?

We can reproduce the problem you reported and have a patch. Look for it in the ImageMagick 6.7.6-8 release.

magick wrote:We can reproduce the problem you reported and have a patch. Look for it in the ImageMagick 6.7.6-8 release.

Don't change anything without further discussion with Anthony. I actually think I am wrong about this.

I think it has been opacity all the time. I think I am confusing using -channel a -separate with -alpha extract. The former gets the opacity and the latter gets the transparency.

But please confirm this.

I think I got confused when trying to answer viewtopic.php?f=1&t=20875

OK. This is now correctly showing the transparency rather than the opacity.