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April 2005
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2005.05.02 14:16 "Re: Color TIFF/JPEG compression questions", by Joris Van Damme
Ed, > ...confusion over RGB vs. YCbCr. > > This image has tags for both : Good of you to notice, I hadn't. Indeed, this point is more foremost then the points I made. > TiffTechNote 2 requires that if the underlying JPEG compression > uses YCbCr Note that Photoshop apparently is able to save CMYK jpeg-in-tiff. Tagdump of one such image generated with Photoshop: SubFileType (1 Long): Zero ImageWidth (1 Short): 3050 ImageLength (1 Short): 2035 BitsPerSample (4 Short): 8, 8, 8, 8 Compression (1 Short): JPEG Technote #2 Photometric (1 Short): Seperated StripOffsets (407 Long): 26480, 50636, 74784, 99608, 124780, 150312,... SamplesPerPixel (1 Short): 4 RowsPerStrip (1 Short): 5 StripByteCounts (407 Long): 24156, 24148, 24823, 25172, 25532, 25662,... XResolution (1 Rational): 305 YResolution (1 Rational): 305 PlanarConfig (1 Short): Contig ResolutionUnit (1 Short): Inch Software (20 ASCII): Adobe Photoshop 7.0 DateTime (20 ASCII): 2004:08:29 15:13:38 DotRange (2 Byte): 0, 255 JpegTables (285 Undefined): 700 (4649 Byte): 60, 63, 120, 112, 97, 99, 107, 101, 116, 32,... Photoshop (17958 Byte): 56, 66, 73, 77, 4, 37, 0, 0, 0, 0, 0, 16, 0,... 34665 (1 Long): 10661832 Upon examination of the first strip data, I see an APP14 marker, and 4 channels specified in both the SOF0 and SOS marker. The 'color transform' byte in the Adobe-style APP14 marker equals 0, which I take to mean that actual true CMYK is encoded in the jpeg data, without additional tranformation. Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html