Question about gimp scaling algorithms

[Ben321]

I notice that there are 2 new scaling algorithms. These are LoHalo and NoHalo. How exactly do these work? I've found nothing on the internet about them (for example academic papers on image scaling algorithms), so I assume that they are exclusive to the Gimp software, have been invented directly by Gimp's developers. So I'm hoping somebody on these forums can explain exactly what calculations it performs. For example, are they based on the Cubic algorithm? Or maybe based on a Sinc function? Or are they based on some kind of AI, that "sees" the image in the same way the human brain sees it, and so actually attempts to make a reasonable effort to scale the image based on what would look the most natural to the human brain?

[rich2005]

It is in the release notes (somewhere)

LoHalo method: when you downscale an image thats less than a half of the original size
NoHalo method: when you do not reduce the size much (rotate, shear or something)
LoBlur method (yet to come) will produce very sharp outcome
LoJaggy (yet to come) is a special method and aimed on reducing jaggyness

Not academic:
A commentry worth a read: https://freedomsponsors.org/issue/78/add...arp-images
which refers to this IM article: http://www.imagemagick.org/Usage/filter/nicolas/ again worth a read.

[Ben321]

(07-18-2018, 10:24 AM)rich2005 Wrote: It is in the release notes (somewhere)

LoHalo method: when you downscale an image thats less than a half of the original size
NoHalo method: when you do not reduce the size much (rotate, shear or something)
LoBlur method (yet to come) will produce very sharp outcome
LoJaggy (yet to come) is a special method and aimed on reducing jaggyness

Not academic:
A commentry worth a read: https://freedomsponsors.org/issue/78/add...arp-images
which refers to this IM article: http://www.imagemagick.org/Usage/filter/nicolas/ again worth a read.

What I mean is what is the actual algorithm used fro NoHalo and LoHalo? Is it even based on a kernel, like other scaling methods? If so, what kernel is it using? If not, what kind of algorithm is it even using?

[rich2005]

You really need to ask the Gimp developers (none here) on this subject. IRC or mailing list https://www.gimp.org/irc.html

AFAIK was a crowdfunding project, to improve/put code by Nicolas Robidoux into Gimp. This code started off in ImageMagick so it is worth going back and looking there.

In Gimp? It is in GEGL somewhere and goes back some time.

For example, part was 'improving the way resampling is applied during transformation'
some code here: https://gitlab.gnome.org/GNOME/gegl/comm...5477c5358e

best of luck