Pngquant is used to to reduce the size (in Kb) of PNG images, by reducing the number of different colors. As much as 70% size reduction is usually achieved.
Most images on this web site are processed with pngquant
This is useful because most images don't need high resolution to look good on the web.
download on ubuntu
pngquant can be downloaded from the ubuntu repository:
sudo apt-get install pngquant
or from the official pngquant homepage
Reduce the number of colours in an image to 32
pngquant 32 myimage.png
You can of course replace 32 with the desired amount of colours - more colours result in higher quality images but the size reduction is not so aggressive.
From my experience, using 64 colours is a good tradeoff between image size and quality.
See this image, its size is 75,6 Kb:
Now this is the image after its number of colours has been reduced to 32, with a command like
pngquant 32 ducati.png:
name.pngas the output image name. Default is to use the same name as the original and append
Instructs pngquant to use as few colours as it can to achieve 99% quality in the output image.
100means best possible quality, i.e. no size reduction at all.