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Interpolation

Aug 27, 2013, 11:53
Post: #1
Interpolation
What is interpolation when scaling images in Gimp? it is under quality. I see there are None, Linear, Cubic, & Sinc (Lanczos 3)... what are these and which one is the best one?? and does it matter which one e.g. are they all the same?
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Aug 27, 2013, 13:12
Post: #2
RE: Interpolation
Oh yeah... those are some real hoopy math formulas. They use them to scale images up or down. The best way I can describe it would be imagine you are scaling an image bigger and you don't want to see bigger pixels. One of the algorithms (I don't know which) blends the colors into a gradient blend.

For example, I made this icon 32x32;

   

Scaled up to 640x640;

   
None

   
Linear

   
Cubic

   
Sync

"I try to stay away from math... it only gets me into more trouble." - Stephen Hawking

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Kubuntu 12.04 - Guild Wars - Retired Paranormal Researcher
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Aug 29, 2013, 06:25
Post: #3
RE: Interpolation
Personally I prefer Cubic over Lanzcos. The reason why Lanzcos is not default is not speed, but because it's considered "broken" by the devs (or at least, that's what Google+ GIMP page owner told me). I made a comparison picture the last time I was deciding between two methods: click and zoom in. (I was only interested in scaling down, btw). You might notice that the lineart stays sharp after Cubic interpolation, but gets washed out with Lanzcos interpolation. On top of that there's some serious haloing going on (above right girl's hair). I dunno, maybe Lanzcos looks better for some images, but not in my experience.

There's been some work on implementing better interpolation methods: https://bugzilla.gnome.org/show_bug.cgi?id=688892
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Aug 29, 2013, 07:19
Post: #4
RE: Interpolation
@Grue: Yeah in your photo, the cubic one looks a lot clearer. Also in wendy's example you can see the top of the bottom left square. In (Sync)Lanzcos, its a little rounded blurrier.

I may change to cubic or linear from now on lol!
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Aug 30, 2013, 04:05
Post: #5
RE: Interpolation
Big Grin Maybe this plugin helps interpolation? http://registry.gimp.org/node/24657

Has anyone here tested it? Looks promising.
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Jun 23, 2018, 17:18
Post: #6
RE: Interpolation
Hi, I was wondering if there was something wrong with the gimp I have. The only interpolation settings I have are none, linear, nohalo and lohalo. I'm trying to make an image smaller while keeping its original quality.ConfusedConfused
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Jun 23, 2018, 19:10
Post: #7
RE: Interpolation
Hi, this forum is dead. We answer questions on Gimp-forum.net. See my sig.

Now answering your questions on
https://Gimp-Forum.net
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