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April 1994

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1994.04.07 14:05 "", by Christoph Wissing
1994.04.07 17:50 "6 Bit TIFF", by Niles Ritter
1994.04.08 09:48 "", by Karsten Spang

1994.04.08 09:48 "", by Karsten Spang

         Hello Christoph

>I encountered a problem when reading some grayscale X-Ray-Images:
>They use 6 Bit per Sample, and I`ve seen in your doc`s:
>    o Class G for grayscale images
>	SamplesPerPixel = 1
>	BitsPerSample = 4, 8
>	Compression = 1 (none) 5 (LZW)
>	PhotometricInterpretation = 0 (Min-is-White), 1 (Min-is-Black)
>so they are not supported, in spite of that palette color images with 6 Bit ar

>Have you any suggestions?
>Of course I could send you such an 6 Bit (uncompressed!) Picture,

If the pictures are uncompressed, it would not be difficult to write
a utility thats reads data in using TIFFReadRawStrip, converts them to
8 bit data (i.e. do bit extraction and multiplication by 4) and writes 
them out again, if this is indeed the problem.

However, you say that the pictures are nearly black. This suggests that the 
problem is different. I guess that your data is indeed 8 bit, but only the 6 
least significant bits are used, this will result in very dark shades. Does your
picture come out in the right size? I suggest that you try multiplying each 
pixel value by 4 before you display the image.

If that doesn't help, include the output from "tiffinfo" in your next posting.

E-mail:                                      Karsten Spang
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