convert -size 256x256 gradient: -rotate 90 -solarize 50% -level 0x50% grad_solarize50a.png
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convert -size 256x256 gradient: -rotate 90 grad.png
convert grad.png -solarize 50% -level 0x50% grad_solarize50b.png
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convert -size 256x256 gradient: -rotate 90 grad.jpg
convert grad.jpg -solarize 50% -level 0x50% grad_solarize50c.jpg
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