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This is fairly theoretical, as it is definitely in the realm of "pixel peeping" and is more or less irrelevant for practical use, but with the increasing popularity of full-width images on websites, I've been experimenting with compression a lot more.

Photoshop save for web seems to be the king here; by carefully sharpening and then manipulating the blur setting, you can achieve outstanding results:

90 quality, 5.4mb:

enter image description here

Lightroom set to "file size less than 1000kb," 858kb:

enter image description here

Photoshop: sharpen, quality 38, blur 0.3: 939kb:

enter image description here

The final image is pretty clearly the winner, it comes closest to the 1mb target while preserving the most quality (visually).

Is there any way to batch-compress files so that they hit these levels of compression while looking as good as the manual, photoshop "save for web" version?

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4 Answers 4

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XnView allows you to batch process files, while adding all sorts of filters.

You can probably achieve something similar as "sharpen, quality 38, blur 0.3" by fiddling a little bit with all the options and filters.

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  • \$\begingroup\$ In this one I would adjust the compression settings in File > Format Adjustments > Writting and select the "best quality" on the Subsampling Factor, for the best results. \$\endgroup\$
    – Rafael
    Commented Feb 24, 2015 at 15:40
  • \$\begingroup\$ "For windows"—too bad, I don't have windows running anywhere at the moment. \$\endgroup\$
    – Ryan
    Commented Feb 25, 2015 at 6:46
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Try Irfanview. press the key 'B' will open a seperate menu for batch conversion. there you can add any no of images, you also have an advanced menu.

http://www.irfanview.com/

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  • \$\begingroup\$ In this program, I would recomend to turn on the checkbox "Disable Chroma Subsampling" on the jpg settings window, this will use a better quality algorithm to compress. \$\endgroup\$
    – Rafael
    Commented Feb 24, 2015 at 15:37
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If you are not afraid of the command line you could use the tools by ImageMagick

mogrify -resize "3000x3000>" -quality 85 *.jpg

3000 here is just a number of pixels, > guarantees either width or height to be of that size. 85 determines the quality of you batch images.

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  • \$\begingroup\$ Welcome to Photo-SE. This is useful and ImageMagick is awesome, but I think this question is about automatically finding the best apparent-quality/size tradeoff for a set of images. Is there a way to do this adapatively with ImageMagick? Is the -resize flag the optimal way to get nice-looking downscaled results? \$\endgroup\$
    – mattdm
    Commented Feb 24, 2015 at 22:54
  • \$\begingroup\$ @mattdm actually, about keeping the highest perceptual (not actual) quality without changing the resolution. \$\endgroup\$
    – Ryan
    Commented Feb 25, 2015 at 5:03
  • \$\begingroup\$ @Ryan Yeah, that's what I mean by "apparent". "Actual quality" is not really a meaningful term. \$\endgroup\$
    – mattdm
    Commented Feb 25, 2015 at 6:41
  • \$\begingroup\$ Sorry, I misinterpreted "size" as pixel dimensions instead of file size. As in "trying to find the best quality / resolution combination for the file size" —which would of course be completely situational and subjective. \$\endgroup\$
    – Ryan
    Commented Feb 25, 2015 at 6:42
  • \$\begingroup\$ I love command line and imagemagick, I use "convert -trim" all the time, but that's not what I'm looking for here. I'm wondering how to make the image look as good as possible under extreme compression without changing the pixel dimensions of the image. \$\endgroup\$
    – Ryan
    Commented Feb 25, 2015 at 6:48
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Mass Image Compressor can convert images in batch. It doesn't have any command prompt, you just point it to a folder and it will compress all images within with given quality and dimension parameters.

Main Window of Mass Image Compressor

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