Using netpbm and GIMP

Install netpbm and GIMP

aptitude install netpbm gimp

Step # 1: Convert logo to ppm raw format

  1. Open your logo using GIMP
  2. Now cut and paste logo in square
  3. Next resize logo by visiting Image > Scale image option. Set pixel size to 16 x 16 or 32 x 32 or 48 x 48.
  4. Next click on File > Save as > Enter file name as favicon.ppm > Click on Save > Raw Encoding > Ok

Step # 2: Convert portable pixmaps into a Windows .ico file

ppmtowinicon -output favicon.ico favicon.ppm

Using imagemagick

Install imagemagick first

brew install imagemagick

and use convert tool

convert -background transparent icon.png -define icon:auto-resize=16,32,48,64,256 icon.ico