ICO converter — open the icon up
An .ico is a container, not an image. This shows you everything inside it and hands each one back as a PNG.
Going the other way? PNG to ICO packs a picture into a multi-size icon, and the favicon generator produces the whole set a website needs.
An icon file holds several images at once
This is the part most converters hide from you. A single .ico is a small archive: a six-byte header, then a directory listing each image it contains, then the image data. A typical Windows application icon holds five or six versions of the same artwork — 16, 32, 48, 64, 128 and 256 pixels square — because Windows picks a different one for the taskbar, the desktop, the Alt-Tab switcher and Explorer's large-icon view.
They are not simply scaled copies of each other. A well-made icon set is redrawn at each size: the 256 px version can carry fine detail, while the 16 px version is usually a simplified silhouette with the detail deliberately removed, because 256 pixels cannot hold a logo. When you extract a set here, differences between the sizes are the designer's decisions showing through, not an error.
PNG entries and BMP entries
Each image inside the file is stored one of two ways, and the readout tells you which. Older icons use a headerless BMP: an uncompressed bitmap, rows stored bottom-up, each row padded to a four-byte boundary, with transparency held in a separate one-bit mask tacked on the end. Since Windows Vista, entries at 256 px are usually stored as a complete PNG instead, which is roughly a tenth the size.
PNG entries are lifted straight out and handed to you unchanged — the readout marks those as extracted byte-for-byte. BMP entries have to be decoded and re-encoded as PNG, which is still lossless, because the bitmap was never compressed in the first place. Both 32-bit entries with a real alpha channel and older 8-, 4- and 1-bit palette entries are handled, including the case where a 32-bit icon leaves its alpha channel empty and the transparency has to be read from the mask instead.
Two quirks worth knowing
The size fields in an icon's directory are a single byte each, so 256 has to be written as zero. Files that record it wrongly cause a lot of icon tools to report a 0×0 image. Here, PNG entries have their true dimensions read out of the PNG header itself, so the directory cannot mislead you.
Cursor files (.cur) use the same structure with a different type flag, and the fields that hold colour-plane and bit-depth information in an icon instead hold the hotspot coordinates. They open here and their images extract normally; the hotspot is simply not something a PNG can carry.
What this page will not do
It will not open an .icns file, which is Apple's entirely different format, and it will not pull icons out of a .exe or .dll — those are resources inside a Windows executable and reading them means parsing the PE format, not the ICO one. If you want to go the other direction and build an icon, PNG to ICO does that.
Common questions
What is actually inside an .ico file?
A directory of entries followed by the image data for each one. Most application icons hold five or six sizes, from 16 px up to 256 px, so that Windows can choose an appropriate one for each place it appears.
Why do the extracted images look different from each other?
Because they were drawn that way. A 16 px icon has only 256 pixels in total, so designers simplify the artwork rather than shrink it. What you are seeing is the original design work, not a conversion artefact.
Does extracting lose any quality?
No. PNG entries are copied out with their bytes unchanged. BMP entries were stored uncompressed, so re-encoding them as PNG is lossless too — the pixels are identical either way.
Can I open a .cur cursor file?
Yes. Cursors use the same container with a different type flag, so the images inside extract normally. The hotspot coordinates cannot be carried over into a PNG.
Why does it say my file is not a valid ICO?
Usually because it is not one. A PNG or JPG renamed to .ico is common and Windows tolerates it in some places, which hides the problem. This page checks the actual header rather than the extension.
Can it pull icons out of an .exe file?
No. Icons inside an executable are Windows PE resources, which is an entirely separate format. This page reads standalone .ico and .cur files only.