Help extract alpha coordinates

[dev.alex89]

I need get size and coordinates of transparent area inside png image.
like 555x560+428+376 in some image.

And it works, but not always

original img http://kartinka.by/imagemagick/r0325.png
convert ./r0325.png -alpha extract -format "%@" info:

and result 1000x1000+0+0 <-- no coords

original img http://kartinka.by/imagemagick/r0051.png
convert ./r0051.png -alpha extract -format "%@" info:

and result 1299x945+0+0 <-- no coords

why on than images alpha extract does not work, how to make it work ?

[snibgo]

If you "-alpha extract" to a new output file, and look at that image with Gimp, and read the values with the eyedropper tool, you will see the values vary. That's why a simple "trim" doesn't trim anything.

"-fuzz X%" will take care of that.

I suppose you want to put an image within the frame. But the frame isn't entirely opaque, so you should probably fix that, eg by alpha extract, threshold and alpha copy.

[dev.alex89]

thanks snibgo, it great, it works !

i think fuzz 10 enough for all same images

[dev.alex89]

Can it take coordinates of two areas from http://kartinka.by/imagemagick/_0103.png

Or it is more difficult ?

[snibgo]

That image has two areas, one in the top half and the other in the bottom half. So "-crop x50%" to split the image.