Losslessly remove chrominance channels iff JPEG is grayscale

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hoanghuynh
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Joined: 2018-01-09T20:05:27-07:00
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Losslessly remove chrominance channels iff JPEG is grayscale

Post by hoanghuynh » 2018-01-09T20:07:57-07:00

Is there a way of losslessly reducing a JPEG image's bit-depth to 8 if it's already in grayscale?
CODE: SELECT ALL

magick convert image image
losslessly chooses the appropriate bit-depth for a grayscale PNG but results in recompression for JPEG. I'm currently using
CODE: SELECT ALL

jpegtran -grayscale -outfile tmpImage
and checking to see if
CODE: SELECT ALL

magick compare -metric rmse image tmpImage NUL

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