Resize image to 80% of "mother"-image

[Bonzo]

I do not think there is a way to do this; if you were using php you could do it using the getimagesize( ) function.

[anthony]

There is not simple direct way to do this. You really need to do the specialized calculation yourself.

When I have time I was planning to enhance settings and arguments to allow the the use of 'format percent escapes' in geometry arguments, which would allow you to extract the width of an image already in memory to resize another image, (see IM Examples, Future proposals) but this not simple and is far down my list of 'things I'm adding to IM', so it may be a long time.