Someone kindly pointed out that the subject line of my last email made it
likely to be caught by a filter.
In case you missed it:
contains the tarred and gzipped folder gimptests.tgz which contains code for
four suggested plug-ins which implement possible replacements for Lanczos.
The README file gives details.
Of the four, IBFNBQH (a brand new method analogous to global cubic splines, but
with a slightly different variational principle and boundary conditions) is the
most likely candidate to replace Lanczos.
If you look at the kingfisher enlargements, you will notice that Lanczos, as
currently implemented in the Gimp, produces artifacts in the top row. None of
the plug-ins have such artifacts. Actually, they have been tested inside and
out, qualitatively and quantitatively, on a variety of images, and are almost
certainly free of "bugs."
Because the top row is cropped out of the enlargement of the other image, this
artifact is not visible.
In addition, although this is of course a matter of taste, I prefer the
"crispness" of IBFNBQH (and EANBQH) to the slight blurriness of Lanczos.
At this point, the plug-ins only enlarge.
I imagine that in order for, say, IBFNBQH to replace Lanczos, it would have to
be fixed so it can resize to arbitrary dimensions. I should be able to do this
in a reasonable amount of time.
David Gowers has suggested using LittleCMS (or GeGL) to linearize colour
profiles during the computation. In our experience, our plug-ins produce good
results when used in a "gamma OBLIVIOUS way." This being said, back of the
envelope computations suggest that "light" haloing is likely to decrease if the
colour profile is properly taken into account (because sRGB has a linear
component near black, "dark" haloing is probably not going to change much for
such images; again, this is from a very rough back of the envelope reasoning).
Given that GeGL will perform all the heavy lifting for the Gimp in the future,
I am not sure that fixing the gamma correction at this point is really
something I want to do. However, I will try to integrate profile information in
the profile if it is felt that it is important.
The current "gamma" versions of the plug-ins use "naive" gamma correction (and
do not take into account the linear piece of sRGB). David's plan is a much
Let me know what you think.
Laurentian University/Universite Laurentienne
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