Intermediate rendering for faster results, and overall smaller file sizes
similar (if not identical) to jpegtran -optimize or PageSpeed.
'-delete', '1--1',
'-trim',
'-background', 'white', '-layers', 'flatten',
'-delete', '1--1',
'-trim',
'-background', 'white', '-layers', 'flatten',
+ '-interlace', 'plane', # progressive
'-resize', "${width}x${height}",
'-quality', '90%',
$source, "jpg:$target"
'-resize', "${width}x${height}",
'-quality', '90%',
$source, "jpg:$target"