AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

1994.04.07 14:05 "", by Christoph Wissing
1994.04.07 10:50 "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 e.

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.

Karsten

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