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by NicolasRobidoux
2018-01-19T16:14:43-07:00
Forum: Digital Image Processing
Topic: Resize and resample in alpha-multiplied light
Replies: 5
Views: 16828

Re: Resize and resample in alpha-multiplied light

A similar type of result: Gamma inserted in a linear pipeline preserves color lines, in the sense that the property of having proportional colors is preserved by the combination. Justification: (R,G,B) is the input image. The pipeline is the composition of a filter1 (a linear color map), a gamma tra...
by NicolasRobidoux
2015-12-27T10:48:10-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 378831

Re: proper scaling of the Jinc filter for EWA use

I don't have the time to check, but it would be nice to compare the graph of the weights obtained with LanczosSharpest2 with the graph of those obtained with RobidouxSharp.
by NicolasRobidoux
2015-12-26T01:33:52-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 378831

Re: proper scaling of the Jinc filter for EWA use

Two comments about my last post: Note how fast the deblurs converge, and the odd-even bracketing. This is unsurprising considering we are fixing things so that the sum of the off-center coefficients is zero: Slightly changing the windowing and adding more weights near the outer edge of the disc does...
by NicolasRobidoux
2015-12-26T01:19:02-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 378831

Re: proper scaling of the Jinc filter for EWA use

Prompted by an mpv video player user https://mpv.io/ (and software developer) who found the EWA LanczosSharpest promising and asked about the optimal values for higher number of lobes, I revised the computation of the "optimal" deblurs after finding suspicious stuff in the original versions. Not a b...
by NicolasRobidoux
2015-12-24T07:00:13-07:00
Forum: Digital Image Processing
Topic: proper scaling of the Jinc filter for EWA use
Replies: 234
Views: 378831

Re: proper scaling of the Jinc filter for EWA use

Regarding the "EWA LanczosSharpest" schemes: What is interesting although not altogether surprising (if you realize that the goal is to have a Jinc-windowed Jinc which with an impulse response as close as possible to a Kronecker delta, and that the outer values are quite small no matter what) is tha...
by NicolasRobidoux
2014-10-05T01:34:24-07:00
Forum: Digital Image Processing
Topic: minimize resize halo by luminance-weighted gamma blending
Replies: 6
Views: 14093

Re: minimize resize halo by luminance-weighted gamma blendin

Alan: Suggestion: For downsampling, try convert input.jpg -set colorspace sRGB -colorspace RGB -define filter:c=SHARPENINGAMOUNT -filter cubic -distort Resize SIZESPECIFICATION -set colorspace RGB -colorspace sRGB output.png or something like that, where SHARPENINGAMOUNT is between 0 and .6666666666...
by NicolasRobidoux
2014-09-20T09:26:25-07:00
Forum: Digital Image Processing
Topic: minimize resize halo by luminance-weighted gamma blending
Replies: 6
Views: 14093

Re: minimize resize halo by luminance-weighted gamma blendin

There is yet another iteration of the script, which has three variants as explained in http://www.luminous-landscape.com/forum ... #msg763245
by NicolasRobidoux
2014-08-29T03:45:43-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Thank you Steve for being so persistent.
This is very informative.
by NicolasRobidoux
2014-08-29T00:25:59-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Is there a way to resize gif's so the file sizes does not become large? Another way is to median filter the input image with a support that roughly matches the square of the downsampling ratio (so if you are downsampling to about 1/3 of the width and height, median filter with a 3x3) then use neare...
by NicolasRobidoux
2014-08-28T09:06:49-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Snibgo: Good idea. (Manana.)
P.S. Hopefully, Steve does not have selection bias.
by NicolasRobidoux
2014-08-28T04:05:03-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Looked some more the line drawing comics results, and EWA RobidouxSharp with luminance-weighted gamma blending is at once more "defined" (some combination of contrast and sharpness) and less aliased than tensor (orthogonal) CatRom with luminance-weighted gamma blending. It's a close call, but on my ...
by NicolasRobidoux
2014-08-27T23:11:27-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Nic, I am not really familiar with the composite operator. Would you mind pointing me to the explanation of the "complex" command line and the rationale of the blending using an alpha mask? (I guess it is meant to thicken the black lines by picking more from the gamma-adjusted downsize.) In this pa...
by NicolasRobidoux
2014-08-27T06:41:01-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Steve: To my eye, the result with the "complex script" and RobidouxSharp -distort Resize looks a touch too sharp. I suggest you try replacing RobidouxSharp by Mitchell or Robidoux and see what you think (think what you see?).
by NicolasRobidoux
2014-08-27T05:23:36-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

Fred: Indeed, the "complex script" with RobidouxSharp -distort Resize looks quite good. Thank you.
by NicolasRobidoux
2014-08-26T23:25:37-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 40188

Re: convert - downscaling comic pages

You may want to test other gammas in the "complex script" than 5/3 (and 3/5). I picked that one because you liked 4/3 and because it should do less damage to dense color patterns that than much larger gamma. My hunch is that >>when downsampling a lot<< gamma 2 (and 1/2) are as far as one should go u...