Recipe to generate Windows ICO files with Graphicsmagick - imagemagick

Question

Based on this question for imagemagick, what is the equivalent for graphicsmagick? Recipe for creating Windows ICO files with ImageMagick?
Also I just want to generate a fully transparent ico file with multiple sizes. I found that there's an xc:none option that works for both, but is there one single command that generates ico files with multiple sizes that is transparent? Otherwise I would have to first create a transparent png file, then create ico files from the png file.

Answer 1

AFAIK, GraphicsMagick doesn't support writing ICO format files - see here.
Just in case anyone knows more about this mad Microsoft format and if it is maybe some sort of multi-page TIF or GIF in disguise that just needs to be renamed, the following would be one way of making a recipe in GraphicsMagick:
#!/bin/bash
{ echo convert image.png mpr:initial;
echo convert mpr:initial -resize 16x16 mpr:16;
echo convert mpr:initial -resize 32x32 mpr:32;
echo convert mpr:initial -resize 48x48 mpr:48;
echo convert mpr:initial -resize 64x64 mpr:64;
echo convert mpr:16 mpr:32 mpr:48 mpr:64 -colors 256 favicon.tif; } | gm batch -prompt off
For the moment, I have created a multi-page TIF as the output file and it contains the four sizes you need - but as I said, GraphicsMagick will not write a ICO file.