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May 2005
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2005.05.26 10:10 "Re: Jpeg and YCbCr", by Jean-yves Le Ridant
> This time i scrathed some codes from rgb2ycbcr.c which is > distributed with libtiff/tools.It works, and i successfully created > the tif image file with compression = COMPRESSION_JPEG & > photometric = PHOTOMETRIC_YCBCR , and can be opened by ACDSEE. Produce a one strip, YCBCR, whatever downsampled image, and tiffcp, tiffdump, or tiffinfo it ... ;-))))) With libtiff 3.7.2 ... > But i still have some thoughts about this things: > Jean Yves: > you said that libtiff already can do this thing(save the tif > image file with compression = COMPRESSION_JPEG & photometric = > PHOTOMETRIC_YCBCR ), > I tried,but failed. Do you have done such things before ? if > so,tell me what's wrong in my codes,or tell me how to do ? thanks . Concerning *pseudo-tag* JPEGCOLORMODE_RGB, I used and use it, and it worked and work fine. What I can imagine, from what I see in code, may be problems relying to order in which you set fields as PLANARCONFIG, PHOTOMETRIC, JPEGCOLORMODE, COMPRESSION ... > [ and i looked at manual page of TIFFWriteScanLine()...,it is > said,there is a bug related to this: > "Writing subsampled YCbCR data does not work correctly because, > for PlanarConfiguration=2 the size of a scanline is not calculated > on a per-sample basis, and for PlanarConfiguration=1 the library > does not pack the block-interleaved samples." Seen this after asked some stupid questions there or/and at bugzilla. Notion of scanline for vertically subsampled data is somewhat hazardous. And that tif_jpeg use it for subsampled data ... ;-( > so i shift to use TIFFWriteEncodedStrip....,(there is no bug > reports in manual page about this function),but it still can't > work.). Strip and tile fonctions, in turn call TIFFVxxxSize fonctions, which give correct result regarding downsampling. So defining scanlinesize as Stripsize(v_sampling) may have some consistance. Best is processing subsampling by stripe and tile. -- Jean-Yves