Downsampling Questions

Started Jul 4, 2014 | Questions thread
Nicolas Robidoux Forum Member • Posts: 84
Re: Downsampling Questions

Pictus wrote:

Downsampling with ImageMagick.

Pictus:

Unsolicited suggestions:

If you've not done so already, could you add EWA LanczosSharpest 4 (not a named ImageMagick method yet) http://www.imagemagick.org/discourse-server/viewtopic.php?f=2&t=25268#p109495 to the collection of available schemes (through linear light for downsampling but ideally not for upsampling, for which the native "perceptual space" of the image is most likely a reasonable and painless choice)?

This is now my favorite sharp scheme. It's reasonably artifact free given how sharp it is.

Currently, my other ImageMagick favorites are EWA Lanczos 3 (yes I know it's soft: add high quality sharpening after the fact), EWA LanczosRadius 3, and EWA Robidoux, RobidouxSoft (not a named IM method yet http://www.imagemagick.com/discourse-server/viewtopic.php?t=19823&p=83900#p109820 ) and RobidouxSharp. I'm still suspicious of the Robidoux methods but a variety of people have found them to be good bang for the buck (esp. given the lack of second halo); I also don't really know methods without a second halo that do as well overall, at least when you don't enlarge too much and don't pixel peep. (For enlarging, the halo free winner may be the NoHalo method of VIPS/NIP2 blended with VSQBS if found to be too aliased. But that's not in ImageMagick. NoHalo and EWA Robidoux are also found in GEGL, the core of bleeding edge GIMP.).

EWA LanczosSharp 3 should be added to this list.

I would stay away from tensor (-resize instead of -distort Resize) ImageMagick methods in your scripts because most people don't have access to an HDRI version of ImageMagick (yet) and the commonly installed implementations, tuned for speed, introduce small artifacts. I think you've already made this choice (namely "stick to EWA"). EWA (Elliptical Weighted Averaging) is generally better anyway.

Of course I understand that you may have different "taste" than I do. The above list is still (!) a work in progress, so it definitely is not definitive For example, I used to think that EWA CatRom was unusable. Not so anymore.

(My apologies for not checking what you have in your scripts right now. "Other cats to whip." <- gallicism)

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