2000.11.13 15:37 "Outstanding Libtiff Issues", by Frank Warmerdam
Folks,
The following two issues were submitted into bugzilla on the weekend (along with a couple of others I dealt with), and look like they deserve attention. However, I am a bit tired after my fight with YCbCr support a few weeks ago.
Anyone interested in pursuing these problems should let me know, and I will happly turn the requests over to them.:
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http://bugzilla.remotesensing.org/show_bug.cgi?id=22
A 16-bit logarithmic luminance presumably has more than 8 bits of linear precision, but currently the only option for automatically converting to "normal" grayscale or RGB is SGILOGDATAFMT_8BIT. (SGILOGDATAFMT_16BIT sounds like it would Do the Right Thing, but instead it converts the integer log(L) to floating-point L and leaves the U and V values, if any, alone.) It would be nice to have an SGILOGDATAFMT_16BIT_INT (or similar) that would convert LOGL and LOGLUV to 16-bit-per-sample, linear, integer grayscale and RGB, respectively. This would be of use in tiff2png and presumably even in tiffcp.
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http://bugzilla.remotesensing.org/show_bug.cgi?id=23
http://www.ai.sri.com/cgi-bin/digitalearth/list.pl?dir=sfbay.oi
The images at the URL above, in varying resolutions, are all tiled YCbCr TIFFs with JPEG compression. Not all tools handle YCbCr TIFFs or tiled TIFFs (or both), so it would be nice if tiffcp did. But despite its lack of diagnostics, when run on such an image with only the -s option, tiffcp produces a tiny file with mangled Y, Cb and Cr components (at least judging by XV's output). For example, the 512x640 level-4 image shrinks from 240k to 33k and changes from a reasonable aerial shot (with black regions indicating no data) to a mostly teal image. Since the tiles are (reported to be) 128x128 pixels, it should be possible to losslessly convert such an image into strips of 512x128 pixels (or so I would imagine--I'm no TIFF expert).
Best regards,
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I set the clouds in motion - turn up | Frank Warmerdam, warmerda@home.com
light and sound - activate the windows | http://members.home.com/warmerda
and watch the world go round - Rush | Geospatial Programmer for Rent