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by NicolasRobidoux
2014-08-26T23:16:35-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

steve___ wrote: ...
I find catrom with ewa too sharp. I have it on my list to try Nicolas'
clone method using catrom without ewa.
Very reasonable. Orthogonal CatRom is a very good orthogonal method.
by NicolasRobidoux
2014-08-26T23:10:01-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Assuming updating IM does not fix the problem: What happens if you put +repage before -depth 8?
by NicolasRobidoux
2014-08-26T23:07:24-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Steve: Are you still using mozjpeg? Make sure your jpeg and png libraries are compatible with ImageMagick. convert -verbose or -version does not necessarily give the whole story because, for example, libjpeg-turbo often installs itself (or, rather, is often installed) as if it was libjpeg (I think; ...
by NicolasRobidoux
2014-08-26T23:03:10-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Is it the +repage command that interacts badly with the bit depth shift? This would be a bug in IM, I think.
Do you really need it? Can you just replace it by -strip?
(As always, really quickly off the top of my head.)
by NicolasRobidoux
2014-08-26T10:55:28-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

For the 16 to 8 bit png result, what do you mean by "worthwhile"? Why would it be better at 8-bits apart from the file size? Steve cares about file size, and an 8-bit png is almost invariably going to be much smaller than a 16-bit one. ----- I am still waiting for Steve's conclusion RE: what works ...
by NicolasRobidoux
2014-08-26T09:50:18-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Steve:
Pretty conclusive.
-----
This is what I remember. (Anyone: correct me if I'm wrong.)
If the input image is 8-bit and you are producing a png, you'll get an 8-bit png.
If the input image is 16-bit and you are producing a png, -depth 8 may be worthwhile.
by NicolasRobidoux
2014-08-25T23:02:56-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

I could be wrong, but I don't think "-depth 16" (or any other number) at the start of the command will make any difference until the image is written to a file. All internal processing is done according to Q and HDRI; a depth number makes no difference. That's what I thought too, but since I was gi...
by NicolasRobidoux
2014-08-25T13:49:10-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

EWA RobidouxSharp winning over orthogonal and EWA Catrom is what I expected.
by NicolasRobidoux
2014-08-25T13:43:06-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

convert \( input.png -depth 16 -set colorspace sRGB -colorspace RGB \) \ \( -clone 0 -gamma 1.666666666666666 -filter RobidouxSharp -distort Resize $res -gamma 0.6 \) \ \( -clone 0 -filter RobidouxSharp -distort Resize $res \) \ -delete 0 \ \( -clone 1 -colorspace gray -auto-level \) \ -compose ove...
by NicolasRobidoux
2014-08-25T13:39:29-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Put -depth 8 right before the output file name if you put a -depth 16 near the beginning. This tells IM that what you want from now on (and "from now on" means "for the output file" since it is just before the output file) is 8-bit per channel. Because you are using HDRI Q16, the result, by the time...
by NicolasRobidoux
2014-08-25T03:43:33-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Steve: There is something that I find quite strange when I compare, say, Catrom-rgb-gamma1.3-web-04.png with RobidouxSharp-rgb-ewa-same... The pixel value of the background is (255,253,229) with (orthogonal) Catrom, and (255,252,217) with EWA RobidouxSharp. You can see it as more yellowed "paper" in...
by NicolasRobidoux
2014-08-24T11:13:49-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

Steve: I'm looking and commenting on this really really fast. My apologies for comments that are not always carefully phrased or even considered. I figure such are better than none.
by NicolasRobidoux
2014-08-24T09:44:52-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

If you want lossless compression, don't use JPEG. Use pngs and pngcrush. However, very high -quality (starts at about 95) is basically impossible to distinguish from lossless unless you make it your mission of seeing the difference (instead of enjoying the content). At -quality 98 no one should comp...
by NicolasRobidoux
2014-08-24T09:40:23-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

The only way to compare JPEG compressors (and resampling methods, for that matter) is to compare visual quality at the same file size and level of being "stripped" (see the documentation for exiftool), meaning that the same amount of metadata must be present in the images.
by NicolasRobidoux
2014-08-24T09:38:07-07:00
Forum: Users
Topic: convert - downscaling comic pages
Replies: 82
Views: 59019

Re: convert - downscaling comic pages

libjpeg-turbo has an interface that clones every version of libjpeg that has been put out (at least the older ones), which I understand is what IM expects. It looks like mozjpeg is not. Mismatched API -> no go.