I want to edit each single size icon in the file manually so that I get exactly what I want.
Is there a tool that will let me have a merged 16x16, 32x32, 48x48 and 64x64 icon that will let me control the content (the exact pixels) of each size?
I've used some favicon generators and uploaded a 48x48 image but my image does not do well when downsized automatically, it needs human intervention from a designer (me).
There are various applications you can download or there are web based editors such as http://www.xiconeditor.com