2011.11.30 13:58 "Re: [Tiff] Inconsistent metadata report for CMYK 8-bit image", by Even Rouault

#################################################################### 2) gdalinfo (from current OSGeo4W package)

C:\> gdalinfo Shadow_cmyk8.tif

Warning 1: TIFFReadDirectory:Unknown field with tag 37724 (0x935c) encountered Driver: GTiff/GeoTIFF

Files: Shadow_cmyk8.tif
Size is 768, 505
Coordinate System is `'
Metadata:
  TIFFTAG_SOFTWARE=Adobe Photoshop CS3 Windows
  TIFFTAG_DATETIME=2011:10:31 14:09:04
  TIFFTAG_XRESOLUTION=72
  TIFFTAG_YRESOLUTION=72
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Image Structure Metadata:
  SOURCE_COLOR_SPACE=CMYK
  INTERLEAVE=PIXEL
Corner Coordinates:

Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  505.0)
Upper Right (  768.0,    0.0)
Lower Right (  768.0,  505.0)
Center      (  384.0,  252.5)
Band 1 Block=768x2 Type=Byte, ColorInterp=Red

  Mask Flags: PER_DATASET ALPHA
Band 2 Block=768x2 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA
Band 3 Block=768x2 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA
Band 4 Block=768x2 Type=Byte, ColorInterp=Alpha

Which one is right?

How many bits per sample and how many samples per pixel is there?

By default, with unusual color spaces like CMYK, GDAL will go through the libtiff RGBA API that does the colorspaces conversions and expose a regular RGBA dataset to GDAL.

You can try however: gdalinfo GTIFF_RAW:Shadow_cmyk8.tif

and with latest trunk (and likely 1.8 too), you'll see:

C:\gdal_trunk\gdal>gdalinfo GTIFF_RAW:Shadow_cmyk8.tif

Driver: GTiff/GeoTIFF
Files: Shadow_cmyk8.tif
Size is 768, 505
Coordinate System is `'
Metadata:
  TIFFTAG_DATETIME=2011:10:31 14:09:04
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
  TIFFTAG_SOFTWARE=Adobe Photoshop CS3 Windows
  TIFFTAG_XRESOLUTION=72
  TIFFTAG_YRESOLUTION=72
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:

Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  505.0)
Upper Right (  768.0,    0.0)
Lower Right (  768.0,  505.0)
Center      (  384.0,  252.5)
Band 1 Block=768x2 Type=Byte, ColorInterp=Cyan

Band 2 Block=768x2 Type=Byte, ColorInterp=Magenta

Band 3 Block=768x2 Type=Byte, ColorInterp=Yellow

Band 4 Block=768x2 Type=Byte, ColorInterp=Black

Band 5 Block=768x2 Type=Byte, ColorInterp=Black

Note the wrong color interpretation was wrong for the last band. The code assumed that for CMYK, you have only 4 bands. I've just fixed that in trunk, and now it reports alpha for band 5.