How can I set a minimum thumbnail size with ImageMagick?

Question

I'm trying to create thumbnails of JPG photos using ImageMagick's convert tool. The thumbnails need to have a defined size (210x159), no blank areas, and the image can be cropped if necessary.

Unfortunately, I only have ImageMagick 6.3.7 available, which doesn't support the '^' geometry modifier (added in v6.3.8-3). Is there another way to achieve this in earlier versions of ImageMagick?

Answer 1

I found a description of how to simulate '^' with older ImageMagic versions. It's not perfect, because the original will be resized 2-3 times, which obviously has the potential to add artifacts and blurring, but it appears to solve the problem.

convert logo: \
        -resize x160 -resize '160x<'   -resize 50% \
        -gravity center  -crop 80x80+0+0 +repage  space_fill.jpg

Here's a rather thorough description of what exactly this does:
http://www.imagemagick.org/Usage/resize/#space_fill