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by NicolasRobidoux
2014-08-24T09:36:18-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

... Of the 12 filters I thought gave the best results, ewa caused 11 of them to become slightly blurry also it increases the file size. The exception was Catrom which became over sharpened. Try -filter RobidouxSharp -distort Resize. Maybe try -filter LanczosRadius -distort Resize if you don't mind ...
by NicolasRobidoux
2014-08-24T03:47:48-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

Steve: I think you forgot to include the originals in your zip file? Or is the orig folder meant to be empty.
by NicolasRobidoux
2014-08-24T00:09:11-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

After much testing with ImageMagick 6.8.8-5 HDRI Q16 I've settled on Catrom with a gamma setting of 1.333333333333333/.75 and no ewa. Here is the syntax I'm using: $ convert infile[0] -quiet -colorspace RGB -gamma 1.333333333333333 -filter Catrom -resize $res -gamma .75 -colorspace sRGB +repage out...
by NicolasRobidoux
2014-08-23T11:37:11-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

I also think that something like this may work well given what you have found to work well, esp. with color: convert \( input.png -depth 16 -set colorspace sRGB -colorspace RGB \) \ \( -clone 0 -gamma 1.666666666666666 -filter RobidouxSharp -distort Resize $res -gamma 0.6 \) \ \( -clone 0 -filter Ro...
by NicolasRobidoux
2014-08-23T07:56:17-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

Thank you Steve. Putting the result of your testing in my "What worked for someone" memory box. P.S. I persist in thinking that an EWA can always be found that does better than any tensor method in a specific situation. Have you tried something like convert infile[0] -quiet -colorspace RGB -gamma 1....
by NicolasRobidoux
2014-08-02T22:23:46-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

On gamma, Q16 and HDRI: If the first gamma is <1, clipping will occur at the bottom (ie in the shadows). For a modest "-gamma 3", the result is horrible with integer Q8, but also noticeable at integer Q16. Results are better at integer Q32, or HDRI at Q8, Q16 or Q32. For a more extreme "-gamma 40",...
by NicolasRobidoux
2014-08-01T12:06:58-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

Fred:
Indeed, there has been some confusion having to do with the fact that when preserving aspect ratio the ellipses are circles.
Question: "Where do ellipses come from?"
Answer: "Ellipses are the offspring of generality."
by NicolasRobidoux
2014-08-01T09:42:17-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

I would suggest that instead of using some numerical measure of "good" which most likely is very loosely correlated with actually looking good, you use your eyes, making lots of comparisons in scenarios similar to the ones that matter.
by NicolasRobidoux
2014-08-01T09:36:39-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

Steve: Your winner is actually sigmoidized EWA Quadratic-Jinc, which has been found, by me and others, to be a good method if you don't like haloing but want strong anti-aliasing. Normally, I would not recommend sigmoidization, but black on white line drawings are perfect for it. P.S. Chester Brown....
by NicolasRobidoux
2014-08-01T07:46:21-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

Start by trying GAMMA = 3 and RECIPROCAL_OF_GAMMA = .333333333333333. The reverse them (GAMMA = .3333333333333 etc). This should give a pretty good idea of the effect. GAMMA = 1 and RECIPROCAL_OF_GAMMA = 1 is wasting cycles to do nothing. Note that if your IM is only 8 bit, this will produce garbage...
by NicolasRobidoux
2014-07-31T22:58:30-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

If you are downscaling and you have thin lines, I suggest you try something like convert input.png -set colorspace sRGB -colorspace RGB -gamma GAMMA -distort Resize SIZE_SPEC -gamma RECIPROCAL_OF_GAMMA -colorspace sRGB ... as a first pass. Going through a gamma space thickens (thin) lines at one end...
by NicolasRobidoux
2014-07-31T22:47:26-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 65215

Re: convert - downscaling comic pages

EWA is of no special help unless you are distorting to some drastically changed view like an extremely tilted perspective. Face-on view don't need EWA. I beg to disagree: The best resampling filters in ImageMagick are EWA methods. So, it you want the best possible results, you "need" EWA. To resize...