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Author Topic: A free high quality resampling tool for ImageMagick users  (Read 230537 times)

alain

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Re: A free high quality resampling tool for ImageMagick users
« Reply #460 on: September 11, 2016, 12:09:26 pm »

Hi Alain,

Feel free to change it for the purpose you use it for. The script can do both downsampling and upsampling, and attempts to preserve the highest quality (in case further processing will be done), which will also result in relatively large file sizes. Actually, 4:4:4 is higher quality, but also larger file size. So for web publishing, you could change it to 4:2:2, or 4:2:0, or 4:1:1, to conserve some file size and speed up the image transfer and page loading times.

Cheers,
Bart
Bart

I've already have several adapted versions of the script, all with superb results.  Thanks again for the script.

I was more inquiring to experiences about using 4:2:0 versus 4:4:4 and what sort of file size changes that can give with almost the same visible quality in "web use".

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Bart_van_der_Wolf

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Re: A free high quality resampling tool for ImageMagick users
« Reply #461 on: September 11, 2016, 01:38:28 pm »

Bart

I've already have several adapted versions of the script, all with superb results.  Thanks again for the script.

I was more inquiring to experiences about using 4:2:0 versus 4:4:4 and what sort of file size changes that can give with almost the same visible quality in "web use".

The resulting file size difference is very hard to predict, and it varies with color and resolution content per image. So an image of the same subject in Blue light or Red light will have significantly different compression factors with 4:2:0, but less different with 4:4:4 .

One can aim for a file size in bytes with ImageMagick, but that mostly varies the compression quality. So that will produce variable output quality. When I want to tweak the file size, I use a Windows program called RIOT (no idea if something similar exists for Mac OS), and that calculates the file size with different subsampling quality and compression settings. If you use that on typical image content then you may find a good average setting.

A program like JPEGmini does it fully automatic, after analyzing the image content it sets the parameters for the visually least noticeable degradation level one aims for, on a per image basis.

Cheers,
Bart
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