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2010.05.11 16:02 "Re: Tiff with varying bit depths", by Thomas Richter
Frank Warmerdam schrieb:
> Thomas Richter wrote:
>> Hi folks,
>>
>> I currently have a need to read and write TIFF files with a varying
>> bit depth. To be specific, this is a BGR565 image packed into TIFF:
>>
>> $ tiffdump out.tif
>> out.tif:
>> Magic: 0x4949 <little-endian> Version: 0x2a
>> Directory 0: offset 8 (0x8) next 0 (0)
>> ImageWidth (256) LONG (4) 1<64>
>> ImageLength (257) LONG (4) 1<64>
>> BitsPerSample (258) SHORT (3) 3<5 6 5>
>> Compression (259) SHORT (3) 1<1>
>> Photometric (262) SHORT (3) 1<2>
>> StripOffsets (273) LONG (4) 1<140>
>> SamplesPerPixel (277) SHORT (3) 1<3>
>> RowsPerStrip (278) LONG (4) 1<64>
>> StripByteCounts (279) LONG (4) 1<8192>
>> SampleFormat (339) SHORT (3) 1<1>
>>
>>
>> Obviously, the library does not support this, but what are my options
>> if I need to read this file? I'm not too keen to write a tiff-parser
>> myself, unless I really really have to - and - I afraid - I really
>> really have to read this file in one way or another.
>>
>> Is there a way to get at least hands on the raw stripe data without
>> the lib falling over? Failing that, what is the patch acceptance policy
>> for libTIFF? Would you accept a patch that adds support for this,
>> probably in a limited way?
>
> Thomas,
>
> Have you investigated using TIFFReadRawTile() to read these tiles? At
> what point does libtiff fail with this file?
Do I misunderstand this? The file isn't tiled, but striped, thus why
would TIFFReadRawTile() help?
Anyhow, I don't even get that far, the code already fails at TIFFOpen():
tfd = TIFFOpen(basename,"r");
if (tfd == NULL)
PostError("failed to open the TIFF file %s\n",basename); // <---
goes here immediately.
(From my code).
> I don't anticipate the regular decompression/decoding logic working with
> such a file in the near future, but I would like to see it be possible
> to fetch the raw tile/strip data without too much difficulty.
That's what I would basically need. The file is uncompressed, i.e. the
data is in a single stripe, bit-packed
as five bits red, six bits green, five bits blue. I assume this is
tiff-conforming, but please look into the
file yourself.
> Can you make one of these files available?
Certainly, please find it attached.
Note that this was created by a custom tiff writer. I *assume* its the
proper way of creating such a tiff file, but I don't know.
Would be great if you could look into this.
Thanks,
Thomas