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2008.02.06 18:40 "[Tiff] tiff library and exif", by Jamie L. Finch
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2008.02.06 20:03 "[Tiff] Bug in tif_print.c for TIFFTAG_REFERENCEBLACKWHITE", by Edward Lam
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2008.02.15 14:36 "[Tiff] bug? JPEGQUALITY seems not to be read correctly", by John
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2008.02.15 14:57 "RE: [Tiff] bug? JPEGQUALITY seems not to be read correctly", by Ed Grissom
- 2008.02.15 15:02 "Re: [Tiff] bug? JPEGQUALITY seems not to be read correctly", by John
- 2008.02.15 17:51 "RE: [Tiff] bug? JPEGQUALITY seems not to be read correctly", by Bob Friesenhahn
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2008.02.15 14:57 "RE: [Tiff] bug? JPEGQUALITY seems not to be read correctly", by Ed Grissom
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2008.02.15 14:36 "[Tiff] bug? JPEGQUALITY seems not to be read correctly", by John
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2008.02.06 20:03 "[Tiff] Bug in tif_print.c for TIFFTAG_REFERENCEBLACKWHITE", by Edward Lam
2008.02.15 14:57 "RE: [Tiff] bug? JPEGQUALITY seems not to be read correctly", by Ed Grissom
There is no place in the header for a "quality" setting. This is not something that is in the JPEG spec or the TIFF spec. What is in both specs is a quality table (q-table). This q-table is generated from the q-setting.
It is difficult to recreate the q-setting that was used to create a q-table.
--
ed grissom
ed.grissom@intergraph.com
-----Original Message-----
From: tiff-bounces@lists.maptools.org [mailto:tiff-bounces@lists.maptools.org] On Behalf Of jcupitt@gmail.com
I think I might have found a bug (or misfeature) in JPEG quality handling.
If I write a file with TIFFTAG_JPEGQUALITY set to 100, it seems to work:
john@mm-jcupitt2:~/pics$ im_copy healthygirl.jpg test.tif:jpeg:100
john@mm-jcupitt2:~/pics$ im_copy healthygirl.jpg test2.tif:jpeg:75
john@mm-jcupitt2:~/pics$ ls -l test*
-rw-r--r-- 1 john john 643587 2008-02-15 14:29 test2.tif
-rw-r--r-- 1 john john 2267003 2008-02-15 14:29 test.tifSo we get a much larger file, as expected. But if I look at the files with tiffinfo, the TIFFTAG_JPEGQUALITY tag is not displayed:
john@mm-jcupitt2:~/pics$ tiffinfo test.tif
TIFF Directory at offset 0x2291ae (2265518)
Image Width: 1166 Image Length: 1944
Resolution: 118.11, 118.11 pixels/cm
Bits/Sample: 8
Compression Scheme: JPEG
Photometric Interpretation: RGB colorYCbCr Subsampling: 2, 2
Orientation: row 0 top, col 0 lhs
Samples/Pixel: 3
Rows/Strip: 16Planar Configuration: single image plane
JPEG Tables: (289 bytes)
and if I copy the file, quality seems to revert to the default (75):
john@mm-jcupitt2:~/pics$ tiffcp test.tif test3.tif
john@mm-jcupitt2:~/pics$ ls -l test*.tif
-rw-r--r-- 1 john john 643587 2008-02-15 14:29 test2.tif
-rw-r--r-- 1 john john 244444 2008-02-15 14:30 test3.tif
-rw-r--r-- 1 john john 2267003 2008-02-15 14:29 test.tifSo it seems that TIFFTAG_JPEGQUALITY is either not being written, or that on reading it is always set to the default 75. This is with libtiff 3.8.2.