2005.05.02 14:16 "Re: [Tiff] 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/
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