1998.02.11 14:58 "Re: AW: Tiff JPEG compression for CMYK images", by Tom Lane
I think CMYK has 4 channels.
So it does, but that's irrelevant. The problem discussed in the message you quoted had to do with asking the JPEG codec to do RGB->YCbCr conversion when the input data didn't have three channels. (If I recall correctly, the upshot was that Bill was trying to apply JPEG compression to indexed-color data, which is not going to work in any case.) For CMYK data, the code is not going to do any colorspace conversion, and it will support any number of channels.
Can i write a class "JPEG" image using libtiff and IJG jpeg-6a with
PhotometricInterpretation = 5 (CMYK)
Commpression = 6 (JPEG)
JPEGProc = 1
JPEGquality = xx
No. libtiff/libjpeg support the newer Compression=7 JPEG scheme defined by TIFF Tech Note #2. Please read the Tech Note to find out why Compression=6 is no good.
regards, tom lane
organizer, Independent JPEG Group