Here is the ImageMagick command I ended up using to get this to work. Essentially I had to adjust the contrast using sigmoidal contrast, to a point that would darken skies enough so when I did a ‘fuzzy crop’, the sky would not get cropped as well.
Well the output of this would look horrible, all I wanted to keep was the size of the output, as well as the offset of the crop to the original. Note below, I use this information formatted using -format '%wx%h%O' info: as a mask to crop my original image.
This way I get to keep my untouched colors and levels, but use the crop from my adjusted one. The blur gave me about an extra 5 pixel white border around the image, which I quickly fixed with a -shave 3x3.
convert -crop `input.jpg +sigmoidal-contrast 5,15 -blur 10 -bordercolor White -border 1 -fuzz 30% -trim -format '%wx%h%O' info:` +repage -shave 3x3 -filter Catrom -size 640x480 -resize 640x480 input.jpg output.jpgBefore
After
Todo
Get the black border images too!