MobileRead Forums - View Single Post - Compress only specified img formats, possible?

tatagi · 01-31-2023, 07:34 PM

I don't know if this is normal but when I used calibre editor tool "compress image losslessly" and checked "enable lossy compression of jpeg images" I personally experienced slow compressions of images in PNG formats somehow.

The quality is set to 80 which in my opinion is the best risk-benefit ratio.

It works well with most of images in jpg/jpeg formats, but for png files, the compression rate is very minimal (only reduction of 3 to 5 percent on average) and the process takes much longer to finish than jpg format.

Furthermore, unlike the option tells about itself, not only jpeg but also other img formats are processed.

The best shot to take is to open "compress image" tool, and then check through each image to select only jpg images to compress and click OK.

It does its job but too time and effort consuming.
I usually prefer to get things done on command line to process files in bulk.

Any ideas?

01-31-2023, 07:34 PM	#1
tatagi Connoisseur Posts: 52 Karma: 10 Join Date: Oct 2022 Device: none	Compress only specified img formats, possible? I don't know if this is normal but when I used calibre editor tool "compress image losslessly" and checked "enable lossy compression of jpeg images" I personally experienced slow compressions of images in PNG formats somehow. The quality is set to 80 which in my opinion is the best risk-benefit ratio. It works well with most of images in jpg/jpeg formats, but for png files, the compression rate is very minimal (only reduction of 3 to 5 percent on average) and the process takes much longer to finish than jpg format. Furthermore, unlike the option tells about itself, not only jpeg but also other img formats are processed. The best shot to take is to open "compress image" tool, and then check through each image to select only jpg images to compress and click OK. It does its job but too time and effort consuming. I usually prefer to get things done on command line to process files in bulk. Any ideas? Last edited by tatagi; 01-31-2023 at 07:36 PM.