I've got something like this so far.. I'm cropping so all thumbs are the exact same size. I haven't settled on 135x180 yet.
Images where width is equal or larger than height:
Code:
convert original.jpg \
-size 720x720 -thumbnail x360 -resize '360x<' -resize 50% \
-gravity center -crop 135x180+0+0 +repage \
-antialias -unsharp 1x1+.05 \
-normalize -contrast -gamma 1.4 -quality 95 \
thumbnail.jpg
Images where height is equal or larger than width:
Code:
convert original.jpg \
-size 720x720 -thumbnail x360 -resize '360x>' -resize 50% \
-gravity center -crop 135x180+0+0 +repage \
-antialias -unsharp 1x1+.05 \
-normalize -contrast -gamma 1.4 -quality 95 \
thumbnail.jpg