Clip PNG with an image mask

[be00k]

I'm trying to clip an PNG image with an image mask.

I tried the following command:

Code: Select all

convert .\src.png .\mask.png -alpha Off -compose CopyOpacity -composite dst.png

When i use a JPEG as source image, everything is working fine. But if i use a PNG image, the output file turns black.

Source Image:


Mask Image:


Output:


Anyone an idea what i'm doing wrong?

[snibgo]

You have "-alpha Off".

This turns off alpha in both images. What colour is revealed when you turn alpha off in the source image?

[be00k]

Ok, my fault! But if i remove the command "alpha -Off" the transparent part in the source image is getting black. So how can i preserve the transparency in the source image?

[snibgo]

You haven't said what result you want.

Your source has transparency. Your mask is greyscale. What pixels in the result should be transparent?

[be00k]

This is what i want to achieve:



The transparent pixels in the source image should stay transparent

(Sorry for my vague descriptions before)

[snibgo]

This nearly gives what you want:

Code: Select all

convert src.png ( +clone -alpha extract mask.png -compose Darken -composite ) -compose CopyOpacity -composite out.png

It's not exact. Perhaps the offsets in src.png are not correct.