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Is there a way to convert an image to ICO format, if the resolution is bigger than 256x256?

I found several programs but none of them was able to convert larger images. The size which I need is 1024x1024.

Nate Barbettini
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D.Steinel
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2 Answers2

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Since the width and height is stored as a single byte each in the ICO image format, it cannot represent images larger than 256×256.

You need to first resize your image.

http://en.wikipedia.org/wiki/ICO_(file_format)#Outline

ЯegDwight
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perh
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  • If you specify the 256x256 size option then Windows Vista and later infer that the PNG format is being used - and the PNG file contained within has its own size specification. I understand right now (Windows Vista through Windows 10) Windows requires the two size specifications to match exactly, but presumably a future version of Windows could defer to the PNG-specified size in order to support larger icons for higher-DPI displays. – Dai Feb 22 '17 at 03:07
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    Strangely when I try to open an ICO produced from a 256x256 PNG using `convert`, my viewer eog fails to load the image, with the message `Compressed icons are not supported`. But it has no problem to display an ICO produced from a 255x255 PNG. So it seems that `convert` decides to change the format setting above 255x255. – Gabriel Devillers Mar 18 '19 at 15:05
  • from the discussion [here](https://en.wikipedia.org/wiki/Talk%3AICO_(file_format)#256x256_support_added_in_Vista_incorrect) it looks like ICO files larger than 256x256 are supported, because the real dimension in the PNG header will be used – phuclv Oct 28 '19 at 04:43
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if you comfortable with actual photo editing software GIMP is a awesome option for this it can take any single image and turn it into a multi-layer icon plus you got all the professional image editing tools at your disposal to customize the images any way you want. and it's %100 free. I use nine image layers on my icons... sizes- 256 128 64 48 40 32 24 20 and 16. to come up with this size formula I just opened a good looking icons .ico file already in use in Windows 11 and this is what I found. oh yeah and don't use compression.

Zantetsuken
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