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2010.04.26 20:12 "Re: Bug in tif_print.c for TIFFTAG_REFERENCEBLACKWHITE", by Edward Lam
Edward Lam wrote:
> I have an 6-Bit RGBA image and using tiffinfo on it gives:
Er, I meant 8-bit here of course.
I also noticed another problem with the number of expected floats for
TIFFTAG_REFERENCEBLACKWHITE in the documentation for TIFFSetField:
http://libtiff.maptools.org/man/TIFFSetField.3tiff.html
where it says:
2*SamplesPerPixel
-Edward
Edward Lam wrote:
> Hi,
>
> This is a repost from awhile back that got no reply which still looks
> like it exists in CVS HEAD. Again, I'd log it in the bug database except
> that I can't seem to currently access remotesensing.org at all.
>
> I have an 6-Bit RGBA image and using tiffinfo on it gives:
>
> $ ./tiffinfo c:/cygwin/tmp/foo.tiff
> TIFF Directory at offset 0x92c3c (601148)
> Image Width: 512 Image Length: 512
> Resolution: 1, 1 (unitless)
> Position: 0, 0
> Bits/Sample: 32
> Sample Format: IEEE floating point
> Compression Scheme: LZW
> Photometric Interpretation: RGB color
> Extra Samples: 1<assoc-alpha>
> Orientation: row 0 top, col 0 lhs
> Samples/Pixel: 4
> Rows/Strip: 2
> Planar Configuration: single image plane
> DateTime: 2008:02:06 13:29:39
> Reference Black/White:
> 0: 0 1
> 1: 0 1
> 2: 0 1
> 3: 2.9389e-039 1.10203e-038
>
> Notice that for the Reference Black/White entry, there's garbage printed
> out in the last pair. According to page 87 of the TIFF6.pdf, the
> ReferenceBlackWhite tag contains 6 rationals (or 3 pairs). tiffinfo
> however is display 4 pairs.
>
> I tracked this down to tif_print.c where we have code like this:
>
> case TIFFTAG_REFERENCEBLACKWHITE:
> {
> uint16 i;
>
> fprintf(fd, " Reference Black/White:\n");
> for (i = 0; i < td->td_samplesperpixel; i++)
> fprintf(fd, " %2d: %5g %5g\n", i,
> ((float *)raw_data)[2*i+0],
> ((float *)raw_data)[2*i+1]);
> return 1;
> }
>
> Notice that i loops from 0 to td_samplesperpixel when I think it should
> be looping from 0 to *3* instead. We similarly hardcode this constant
> for this tag in other places.
>
> One might think that perhaps the SamplesPerPixel tag should be 3 for
> RGBA images but I think the TIFF 6 spec clearly says that
> SamplesPerPixel *includes* ExtraSamples in the description for
> ExtraSamples (page 31) as well as the note about it on page 27.
>
> Thanks,
> -Edward
>
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