Legacy ImageMagick Discussions Archive

Hi,

I got a 24bits png and I want to get a mask (1bit) for color X (say '#aabbcc')

I want output pixel to be black where input pixel was '#aabbcc'
and output pixel to be white for any other pixel input


I tweaked the exemple at viewtopic.php?t=13602

convert rmgcb.png \
\( -clone 0 \
-transparent '#aabbcc' \
-alpha extract \
-fill white -opaque white \
-transparent black \) \
-compose over -composite \
rmgcb_red_yellow_blue.png

but the outpixel are still colorfull

thank you

You make #aabbcc transparent, then "-alpha extract" makes black where the pixels were #aabbcc, and white otherwise.

That's what you want, isn't it?

Then you do other stuff.

exactly what I needed.
thank you snibgo.

snibgo wrote: ↑2016-11-10T07:55:37-07:00 You make #aabbcc transparent, then "-alpha extract" makes black where the pixels were #aabbcc, and white otherwise.

That's what you want, isn't it?

Then you do other stuff.

Code: Select all

convert rmgcb.png \
-transparent '#aabbcc' \
-alpha extract \
rmgcb_red_yellow_blue.png

In my case, the original image (rmgcb.png) already has some transparency, and that is getting mixed with the color I want to extract the mask for. Is there any way to fix this? I tried turning off the transparency, but than this defaults to a black background, which is a problem in cases when I want to extract the black color to a mask.

What do you want to happen to the pixels that are initially transparent?

They shouldn't be included in the mask, i.e. the final mask should be black wherever the original was transparent.