PNG to Favicon.

Three PNG designs, nine decoded favicon frames

These are new, opaque, square test images, not the transparency bands or padding samples used elsewhere on this site. We made each source at 256 × 256 pixels: a thick white plus on blue, a black one-pixel grid on white, and three separated coloured bars. Every source and downloaded result is linked below so the test can be repeated without recreating the artwork.

On 2026-11-03 in Asia/Shanghai, Chromium 156.0.8078.4 opened the public PNG to ICO converter. For each source we kept only 16, 32 and 48 selected, generated the ICO, and saved the actual browser download. We read the saved ICONDIR and every ICONDIRENTRY, checked that each offset plus length stayed inside the file, extracted each PNG payload, and decoded that payload again. The dimensions in this table came from decoded images, not filenames or preview labels.

• bold-plus: source PNG → downloaded ICO, 868 bytes total; three entries and a 54-byte header/directory. Open the linked-icon test tab.
• fine-grid: source PNG → downloaded ICO, 550 bytes total; three entries and a 54-byte header/directory. Open the linked-icon test tab.
• three-bars: source PNG → downloaded ICO, 765 bytes total; three entries and a 54-byte header/directory. Open the linked-icon test tab.

All three saved files contain exactly three image entries, at 16 × 16, 32 × 32 and 48 × 48 pixels. Their six-byte ICONDIR and three sixteen-byte directory entries occupy 54 bytes before the first PNG. For bold-plus, 243 + 207 + 364 payload bytes + 54 directory bytes = 868 total bytes. The same accounting gives 550 bytes for fine-grid and 765 for three-bars. No entry is a renamed source PNG.

A valid file does not guarantee readable small artwork

The grid source uses one black pixel every sixteen source pixels in both directions. Its decoded 16-pixel frame has 0 near-black pixels and 256 near-white pixels out of 256. Here near-black means all RGB channels below 32, and near-white means all channels above 223. At 32 pixels it has 256 near-white pixels out of 1024; at 48 it has 1024 out of 2304. Those are measurements of these output files, not a statement about which frame every browser chooses. A source with tiny lines can export successfully while losing the dark lines that made it recognisable.

Repeat the file and linking checks

1. Download one source PNG above and run it through the converter with 16, 32 and 48 selected. Save the ICO instead of inspecting only its preview.
2. Read the entry count at byte offset 4 as a little-endian sixteen-bit value. Starting at offset 6, each sixteen-byte directory entry gives its width, height, payload length and payload offset. Decode the extracted bytes and compare the dimensions and totals above.
3. Open the corresponding linked-icon test tab. Its HTML contains a rel="icon" link to the downloaded ICO. It contains no in-page icon image; a picture in an article is not evidence of a browser-tab favicon.
4. For your own site, publish the ICO, paste the generated link into that page's head, then open a fresh tab. Check that the icon URL returns the ICO rather than an HTML error page.

Display-test scope: The three linked-icon pages were opened in desktop Chrome. Native tab-strip visual inspection was blocked by the computer-control URL safety check, so this record does not certify their toolbar appearance, the chosen frame, dark-mode rendering, or a physical phone on cellular data. Use the linked tabs to inspect the real files in your browser; the pixel and byte results above describe downloaded files only.

Raw measurements and SHA-256 hashes. This is a reproducible test of this converter and these fixtures, not proof that no other website has ever tested favicons.