image processing - Recommendation for compressing JPG files with ImageMagick

Question

I want to compress a JPG image file with ImageMagick but can't get much difference in size. By default the output size is bigger than the input. I don't know why, but after adding some +profile options and setting down the quality I can get an smaller size but still similar to original.

The input image is 255kb, the processed image is 264kb (using +profile to remove profiles and setting quality to 70%). Is there any way to compress that image to 150kb at least? Is that possible? What ImageMagick options can I use?

Answer 1

I use always:

• quality in 85
• progressive (comprobed compression)
• a very tiny gausssian blur to optimize the size (0.05 or 0.5 of radius) depends on the quality and size of the picture, this notably optimizes the size of the jpeg.
• Strip any comment or EXIF metadata

in imagemagick should be

convert -strip -interlace Plane -gaussian-blur 0.05 -quality 85% source.jpg result.jpg

or in the newer version:

magick source.jpg -strip -interlace Plane -gaussian-blur 0.05 -quality 85% result.jpg

Source.

From @Fordi in the comments (Don't forget to upvote him if you like this): If you dislike blurring, use -sampling-factor 4:2:0 instead. What this does is reduce the chroma channel's resolution to half, without messing with the luminance resolution that your eyes latch onto. If you want better fidelity in the conversion, you can get a slight improvement without an increase in filesize by specifying -define jpeg:dct-method=float - that is, use the more accurate floating point discrete cosine transform, rather than the default fast integer version.