Recommendation for compressing JPG files with ImageMagick

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?

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.

I'm using the Google Pagespeed Insights image optimization guidelines, and for ImageMagick they recommend the following:

-sampling-factor 4:2:0
-strip
-quality 85 [it can vary, I use range 60-80, lower number here means smaller file]
-interlace
-colorspace RGB

Command in ImageMagick:

convert image.jpg -sampling-factor 4:2:0 -strip -quality 85 -interlace JPEG -colorspace RGB image_converted.jpg

With these options I get up to 40% savings in JPEG size without much visible loss.

Just saying for those who using Imagick class in PHP:

$im -> gaussianBlurImage(0.8, 10);      //blur
$im -> setImageCompressionQuality(85);  //set compress quality to 85

Once I needed to resize photos from camera for developing:

• Original filesize: 2800 kB
• Resolution: 3264x2448

Command:

mogrify -quality "97%" -resize 2048x2048 -filter Lanczos -interlace Plane -gaussian-blur 0.05 

• Result filesize 753 kB
• Resolution 2048x2048

and I can't see any changes in full screen with my 1920x1080 resolution monitor. 2048 resolution is the best for developing 10 cm photos at maximum quality of 360 dpi. I don't want to strip it.

edit: I noticed that I even get much better results without blurring. Without blurring filesize is 50% of original, but quality is better (when zooming).

I would add an useful side note and a general suggestion to minimize JPG and PNG.

First of all, ImageMagick reads (or better "guess"...) the input jpeg compression level and so if you don't add -quality NN at all, the output should use the same level as input. Sometimes could be an important feature. Otherwise the default level is -quality 92 (see www.imagemagick.org)

The suggestion is about a really awesome free tool ImageOptim, also for batch process.
You can get smaller jpgs (and pngs as well, especially after the use of the free ImageAlpha [not batch process] or the free Pngyu if you need batch process).
Not only, these tools are for Mac and Win and as Command Line (I suggest installing using Brew and then searching in Brew formulas).