ICO to PNG Converter

An .ico file is a small archive: the same icon drawn at several sizes, from 16 × 16 for lists to 256 × 256 for large desktop icons, each with its own transparency. Websites, slides and design tools want PNG instead. This tool opens the icon (or a .cur cursor), saves every image inside it as a separate PNG with the transparency intact, and lists their sizes and bit depths — in your browser, without uploading anything.

How to use this tool

1. Drop one or more .ico or .cur files into the box.
2. Choose every size (downloaded as a ZIP) or only the largest image.
3. Check the table: it lists each image's size, bit depth and how it was stored.
4. Download the PNG files.

Formula

ICONDIR (reserved 0, type 1 = icon or 2 = cursor, image count) → one 16-byte entry per image (width and height — 0 means 256 — colour count, planes or hotspot X, bit count or hotspot Y, byte length, offset) → the image data.

Since Windows Vista an entry may simply be a PNG file, which is copied out unchanged. Older entries are bitmaps: a header with the height doubled, an optional palette, the colour pixels stored bottom-up in rows padded to 4 bytes, then a 1-bit AND mask that marks transparent pixels. 1-, 4-, 8-, 16-, 24- and 32-bit entries are decoded; a 32-bit entry uses its own alpha channel unless that channel is empty.

Example

A typical Windows application icon holds 16, 32, 48 and 256 px images. Every size gives app-16x16.png, app-32x32.png, app-48x48.png and app-256x256.png in a ZIP; "Only the largest image" gives just app-256x256.png. If the same size appears twice, for example 32 px at 8-bit and 32-bit, the bit depth is added to the file name.