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 
better one.

Let me know what you think.

Nicolas Robidoux
Laurentian University/Universite Laurentienne
Gimp-developer mailing list

Reply via email to