What is the max possible size of an 32x32px .ico file?

Question

I'm making a favicon.ico script, and I need to know the max amount of bits possible.

assuming only 1 icon in the .ico ? – jk. Mar 12 '10 at 11:42 — jk., Mar 12 '10 at 11:42
The maximum size it will have will be 32x32 pixels. - jk – Camilo Martin Dec 04 '11 at 19:54 — Camilo Martin, Dec 04 '11 at 19:54

Oded · Answer 1 · 2010-03-12T14:37:47.347

5

It depends on the number of colours you are using.

For 8bit (256 colours):

32 * 32 * 8 = 8192 bits
8192 / 8 = 1024 bytes
1024 bytes = 1Kb

For 32bit (16.7 million colours):

32 * 32 * 32 = 32768 bits
32768 / 8 = 4096 bytes
4096 bytes = 4Kb

See wikipedia.

edited Mar 12 '10 at 14:37

answered Mar 12 '10 at 11:41

Oded

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score 4 · Accepted Answer · answered Mar 12 '10 at 11:39

4

It maxes out at 32 bits per pixel, 24 RGB plus alpha transparency, so that would be 32 x 32 x 32, or 32768 bits.

So 4096 bytes (4K).

answered Mar 12 '10 at 11:39

paxdiablo

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Of course, there are also headers, and there could be more than one size/color depth in an icon... – SamB Feb 17 '11 at 17:14

score 2 · Answer 3 · answered Mar 12 '10 at 14:46

2

In theory, a single ico file can contain up to 65,535 images (see header description). That would mean that the maximum number of pixels could be as large as 65535*32*32, which at 4 bytes per pixel comes to 268,435,456 bytes.

answered Mar 12 '10 at 14:46

unwind

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Such a file would be pretty silly, though -- there'd be no basis for the consuming program (app or OS) to prefer any particular image, if they all have the same color depth and size! (Also, headers take space too.) – SamB Feb 17 '11 at 17:16

What is the max possible size of an 32x32px .ico file?

3 Answers3