Image compression

Image files will usually have the most impact on the speed of your websites (aside from Ad/tracker scripts). Learn to slim down your images using the ubiquitous ImageMagick to make your websites faster on slow internet connections.

Image network speed

For the examples, I decided to use this public domain image.

Compressed image of a cat

There are many ways to decrease image size using ImageMagick, the simplest is to use the -quality option, which will compress the image without changing the resolution. This option takes the value you want to compress by (between 1 and 100, the lower the value, the lower the file size). For example:

convert in.jpg -quality 50 out.jpg

Compressing the example image above results in the following file size changes:

  Quality    Size
  ---------- ------
  Original   2.1M
  90         1.7M
  80         844K
  70         588K
  60         448K
  50         368K
  40         308K
  30         248K
  20         184K
  10         116K

Due to the images high resolution, it is usable in this website even when highly compressed (30% quality, still looks decent in my opinion).