ICO is a container format: a single .ico file can hold multiple rasters at different sizes. Sometimes you have an ICO and you want the underlying PNGs — to redesign the favicon, to inspect the icon's design, or to feed into a build tool that expects PNGs. This tool unpacks the ICO into its component images.
ICO container format
A Windows ICO is a directory of image entries. Each entry has a size (in pixels), a color depth, and a payload — the payload can be either an uncompressed BMP (older ICOs) or an embedded PNG (Vista+). The extractor detects both formats and outputs a standalone PNG for each entry.
Multiple sizes → multiple PNGs
A typical favicon.ico contains 16×16, 32×32, and 48×48. Modern ones may also include 64, 128, and 256. Each size is extracted as a separate filename-16.png, filename-32.png, etc. The tool preserves transparency and color depth exactly.
What to do next
Common workflows after extraction: (1) Redesign in a raster editor, then rebuild the ICO with the Favicon Generator. (2) Vectorize the largest size with PNG-to-SVG for a modern favicon.svg. (3) Convert individual sizes to WebP for use elsewhere. The extractor is the entry point; the rest of the pipeline is up to you.