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2009.12.10 20:55 "Re: YCbCr", by Steve Mills
On Dec 10, 2009, at 14:32:14, Joris Van Damme (AWare Systems) wrote: > It does, in the sense that it is LibTiff's wrong way to try and support > the result that you're after in this particular case. Do thorough testing, > and if it works for you, it works for you. > > So, what you were getting was not channel-order-inversed RGB, but YCbCr, > actually. And that is what the Photometric said you'd get. Only if the > Photometric is YCbCr, and the compression is JPEG, can you suddenly turn > this into RGB by using this magical out-of-the-blue pseudo-tag. But you'll > have to remember to have your code thoroughly check for these conditions, > and use the magical pseudo-tag. So you're saying I can NOT just ALWAYS set this tag? I tried setting it only after reading had begin and we were reading tags to get color space, pixel size, etc, but it did not work. Moving the tag-setting to right after TIFFClientOpen made it work. Are you saying that we will get incorrect results for other cases that are NOT YCbCr jpeg-compressed? The same tester just sent me a cymk jpeg-compressed tiff (PC byte order, created in Photoshop CS3). It is showing up wrong. Each pixel should be cmyk 0%,99%,99%,0% (that's what I see in Photoshop - the entire file is red, not a great test file, but that's what he sent), but the hex values I see for each pixel are 4d,55,ff,00 after we call TIFFReadScanline. I tried making my own test document in Photoshop CS4, but my files are showing up correctly. They're much smaller and contain pixels colored cyan, magenta, yellow, and black. _________________________________________________________ Steve Mills Me: 952-401-6255 Senior Software Architect MultiAd smills@multiad.com www.multi-ad.com