** Changed in: gimp
Status: Confirmed => Fix Released
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https://bugs.launchpad.net/bugs/16128
Title:
Wide color channels in Gimp
Status in The GNU Image Manipulation Program (GIMP):
Fix Released
Status in “gimp” package in Ubuntu:
Triaged
Bug description:
After discussing with some graphics people in the community, it has come to my
attention that Gimp only supports 8 bits per color channel (bpc), totalling 32
bits RGBA. Architecturally, Gimp is not easily expanded to wider color
channels
such as 16 or 32 bpc; however, it is possible. Previously, some developers
created a program called "cinepaint," a Gimp fork that supported 16 and 32 bpc
color spaces. Unfortunately the project eventually halted and does not
support
the range of features of newer Gimp.
* http://cinepaint.sourceforge.net/
Although humans can't tell the difference between 8bpc and 16bpc, mathematical
algorithms can. In particular, certain mathematics used to touch up images or
blend colors can result in a visual artifact called "banding," where visible
differences in lumance appear in the image where there previously were none,
often resulting in what look like bands of areas with different gammas or
brightnesses. To prevent this, the color space can be increased so that the
bands occur over ranges so small that when reduced back to 8 bpc color space,
they are lost with the extra information in the other 8 or 24 bits. In other
words, rounding is saved for the end of the process.
To achieve the best effect, images should be stored and operated on in a full
range color space. Rounding down to an 8 bpc color space should only be done
when the image is finally exported to a standard 24 or 32 bit format such as
PNG, MNG, or JPEG. This allows the results of previous large color space
operations (i.e. image effects such as blurring and glass lenses) to retain
their extra information so that more effects can be added on top of them
without
visible artifacts, further reducing or even eliminating banding.
This bug should not be a high priority, as it would require the Ubuntu
developers to massively patch the internal architecture of Gimp, and then to
convince the Gimp mainline developers to accept the patches. Historically,
the
Gimp mainline developers apparently have inverted interest in (i.e., will
fight
against) widened color spaces; however, professional graphics artists
understand
that at least 10 bpc of color space (i.e. 40 bit instead of 32) are needed to
produce quality images, and hence have been moving off Gimp and onto
Photoshop.
Bigger is better; even high-end 3D graphics cards operate in 128 bit color
(32bpc) (as noted in John Carmack's .plan file from when he was writing
Doom3).
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