When this tool is useful
Extracting a Windows icon for inspection or building a conventional favicon or desktop icon from deliberately prepared square PNG sizes.
How local processing works
The browser validates the ICO directory and byte ranges, lists supported embedded PNG or bitmap entries with their declared dimensions, and either decodes one entry or writes selected square PNG payloads into a new deterministic icon directory.
How to use it
- Prepare the source and limits: Keep an unchanged source and review the accepted format, dimensions, frame or page budget, and output choices. Extracting a Windows icon for inspection or building a conventional favicon or desktop icon from deliberately prepared square PNG sizes.
- Process locally: Run the documented bounded operation in this browser and stop when the decoder reports an unsupported structure. The browser validates the ICO directory and byte ranges, lists supported embedded PNG or bitmap entries with their declared dimensions, and either decodes one entry or writes selected square PNG payloads into a new deterministic icon directory.
- Download and verify: Inspect every intended icon size against the source, check transparent and antialiased edges on light and dark backgrounds, test the ICO in the actual Windows, browser, or application target, and retain the individual PNG masters.
Important limitations
Unsupported bit depths, color masks, cursor hotspots, malformed offsets and very large entries are rejected. ICO consumers choose sizes differently, 256 is encoded by a zero directory byte, transparency can vary between PNG alpha and legacy masks, and packaging PNG bytes does not invent sharper detail at missing sizes.
Verify the downloaded result
Inspect every intended icon size against the source, check transparent and antialiased edges on light and dark backgrounds, test the ICO in the actual Windows, browser, or application target, and retain the individual PNG masters.
Private by design
Your files stay in this browser. The tool does not upload the source or output to our servers.
Questions and answers
When is this workflow useful?
Extracting a Windows icon for inspection or building a conventional favicon or desktop icon from deliberately prepared square PNG sizes.
What does local processing do?
The browser validates the ICO directory and byte ranges, lists supported embedded PNG or bitmap entries with their declared dimensions, and either decodes one entry or writes selected square PNG payloads into a new deterministic icon directory.
Which format limits matter?
Unsupported bit depths, color masks, cursor hotspots, malformed offsets and very large entries are rejected. ICO consumers choose sizes differently, 256 is encoded by a zero directory byte, transparency can vary between PNG alpha and legacy masks, and packaging PNG bytes does not invent sharper detail at missing sizes.
How should I verify the download?
Inspect every intended icon size against the source, check transparent and antialiased edges on light and dark backgrounds, test the ICO in the actual Windows, browser, or application target, and retain the individual PNG masters.