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Image Scaling Interpolation options
#1
1) Using Gimp 2.10.2  2) Mint 18.3
 
With Gimp 2.8 I had the option of selecting "Sinc Lanczos2" as the interpolation policy under "Image/Scale Image."
With Gimp 2.10 the options are "None," "Linear," Cubic," "NoHalo," and "LoHalo."  "Sinc (Lanczos3)" as recommended on the Gimp website is not offered as an option. I have been using "NoHalo" which seems to be OK, but I'd feel more comfortable using the Sinc (Lanczos3) because of the recommendation. Is there a way to install that profile or policy?
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#2
No, you can't add back Sinc/Lanczos (unless you are a pretty good C programmer). But developpers have discussed the merits of LoHalo/NoHalo and found that they performed better than Sinc/lanzos (which was recommended only because it was better than the available alternatives in 2.8).
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#3
(06-21-2018, 11:25 PM)Ofnuts Wrote: No, you can't add back Sinc/Lanczos (unless you are a pretty good C programmer). But developpers have discussed the merits of LoHalo/NoHalo and found that they performed better than Sinc/lanzos (which was recommended only because it was better than the available alternatives in 2.8).

OK. Good to know. Thank  you for the information.
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#4
(06-21-2018, 11:25 PM)Ofnuts Wrote: No, you can't add back Sinc/Lanczos (unless you are a pretty good C programmer). But developpers have discussed the merits of LoHalo/NoHalo and found that they performed better than Sinc/lanzos (which was recommended only because it was better than the available alternatives in 2.8).

I am a professional image analyst.  LoHalo and NoHalo are terrible in comparison to Sinc/Lanczos.  Period.  I need to find another way to downsample my (scientific) images now.  In what manner are they similar?

I just upgraded 2.8 to 2.10 to get handle transform.  But the **Halo methods look totally blurry for the same image types, same scaling.  Very large downsample... like 10:1.
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#5
Quote:...Very large downsample... like 10:1

The only lanczsos scaling I have come across in Gimp 2.10 comes from the gimp_gmic_qt plugin, http://www.gmic.eu One of the filters: Layers -> Multiscale Operator.

   

Always some snags, works in percentages not absolute pixel sizes and as the name 'multi' layers. You can get out 2 layers of the same size as a new image, effectively a single layer. The gmic operation could be scripted if required to make it more convenient. Not exactly the same as the equivalent Gimp 2.8 scale but close. Comparison attached.


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#6
(12-09-2020, 09:32 AM)rich2005 Wrote: Not exactly the same as the equivalent Gimp 2.8 scale but close. Comparison attached.

It seems that in version 2.8 the pixalization is less noticeable. But that with an increase of 800%.
I practically could not see differences with visualization in 100%.
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#7
Sinc (Lanczos3) in GIMP 2.8 also had a nasty habit (certainly if used with rotation of the image) of leaving pixels near the corners that had lower alpha values than pixels that were even closer to the corners. Some of the pixels that were closer to the corners could have alpha values of 255. This made removal of the (semi-)transparent areas using a script difficult.
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