How to extract different sizes of an icon from favicon.ico file?

I want to extract different sizes (if avail开发者_开发知识库able) from favicon.ico file and save each to separate .png files (e.g. favicon16.png, favicon32.png etc.) using PHP. How to achieve that?

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A class to extract icons from a .ico file as PNG files

I know not everybody likes phpclasses.org; but if it works, use it