I propose to add color.CMYK and image.CMYK types to Go 1.5, in order
to decode CMYK JPEG images. They're very rare (of my web crawl of
169,732 JPEGs, only 52 of those, or 0.03%, are CMYK JPEGs), but
supporting these has come up a few times (issue #4500).

https://go-review.googlesource.com/#/c/4800/ has the image and
image/color changes.

https://go-review.googlesource.com/#/c/4801/ has the image/jpeg changes.

Another change, not done yet, will affect image/draw.

The design is straightforward, mimicking the color.RGBA and image.RGBA
types. This means that each image.CMYK pixel is packed into 4
continuous bytes, as opposed to image.YCbCr's separate planes to
accomodate subsampling. I suppose you could argue either way, but I
think the jpeg decoder is easier with the like-RGBA packing, since
decoding YCbCrK images require converting from planes to packs anyway,
and non-uniform subsampling ratios for CMYK images seem more
accidental than deliberate.

Color profiles are out of scope.

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postedFeb 13, '15 at 7:28a
activeFeb 13, '15 at 7:28a

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Nigel Tao: 1 post



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