LibTiff Mailing List

• TIFF and LibTiff Mailing List Archive
• April 2010

• Previous Thread
• Next Thread

• Previous by Thread
• Next by Thread

• Previous by Date
• Next by Date

Contact

The TIFF Mailing List Homepage
Archive maintained by AWare Systems

Thread

2010.04.26 20:12 "Re: [Tiff] 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

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.