Package: openimageio-tools
Version: 1.0.0+dfsg0-1
Severity: normal
[Sorry if this is a bit long; issues involving image gamma are always
kind of confusing, so I'm trying to be as explicit and verbose as
possible...]
Given:
1. A typical PNG image file, "foo.png", which was encoded using a
standard encoding gamma correction value of 1/2.2 (0.4545), and
has an explicit PNG gAMA chunk recording that value.
2. A JPEG file, "foo.jpg", produced from "foo.png" file using the
imagemagick command "convert foo.png foo.jpg".
3. Another PNG file, "foo2.png", produced from "foo.jpg" using the
imagemagick command "convert foo.jpg foo2.png"; note that foo2.png
_doesn't_ have an explicit gAMA chunk.
Then:
* Most image display programs (imagemagick, eog, geeqie, qiv, ...)
display all of the files identically. In other words, they assume
that the encoding gamma correction value is 1/2.2 (0.4545) for both
JPEG files, and PNG files without an explicit gAMA chunk.
* "iv foo.png" and "iv foo2.png" displays the image "correctly"
(matching what other image-display programs do), suggesting that it
assumes a default encoding gamma correction value of 1/2.2 for PNG
files.
* _However_, "iv iv.jpg" displays the image much too dark, unlike all
other programs. By using the ")" key-command to change the "gamma"
value to 2.2, the image then looks correct.
=> Thus the bug: it appears that iv assumes an encoding gamma
correction of 1.0 for JPEG files, which does not match standard
practice.
[As an aside, the term "gamma" value displayed in the iv GUI is a bit
confusing; it appears to actually be "encoding gamma correction
divided by display gamma correction."]
Thanks,
-Miles
-- System Information:
Debian Release: wheezy/sid
APT prefers unstable
APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (50,
'experimental')
Architecture: amd64 (x86_64)
Kernel: Linux 3.2.0-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=ja_JP.utf8, LC_CTYPE=ja_JP.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages openimageio-tools depends on:
ii libboost-filesystem1.49.0 1.49.0-2
ii libboost-regex1.49.0 1.49.0-2
ii libboost-system1.49.0 1.49.0-2
ii libboost-thread1.49.0 1.49.0-2
ii libc6 2.13-27
ii libgcc1 1:4.7.0-3
ii libgl1-mesa-glx [libgl1] 7.11.2-1
ii libglew1.7 1.7.0-3
ii libglu1-mesa [libglu1] 7.11.2-1
ii libilmbase6 1.0.1-4
ii libjpeg8 8d-1
ii libopenexr6 1.6.1-5
ii libopenimageio1.0 1.0.0+dfsg0-1
ii libpng12-0 1.2.49-1
ii libqt4-opengl 4:4.7.4-3
ii libqtcore4 4:4.7.4-3
ii libqtgui4 4:4.7.4-3
ii libstdc++6 4.7.0-3
ii libtiff4 3.9.6-2
ii libx11-6 2:1.4.4-4
ii libxext6 2:1.3.0-3
ii zlib1g 1:1.2.6.dfsg-2
openimageio-tools recommends no packages.
openimageio-tools suggests no packages.
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