PNG to ICO Converter: Do PNG Color Types Change the Result?

One decoded image, four PNG color types

The 64×64 source artwork is a simple opaque grayscale drawing. It was saved as RGB (PNG color type 2), RGBA (type 6 with every alpha value at 255), indexed color (type 3), and grayscale (type 0). The four files differ in PNG storage type and byte length, but a local decode check confirmed that every RGBA pixel was identical.

Each file was run once through the pngtoicotool browser converter and once through ConvertICO.com. The third-party page's option to display a result in its Recently Converted Icons gallery was left unchecked. The ICOs were downloaded and inspected locally; no page-displayed size was used as the measured file size.

The decoded ICO layers matched for this sample

All eight downloaded ICOs contained 16×16, 32×32, 48×48, 64×64, 128×128, and 256×256 layers. For each converter, the four files had the same SHA-256 hash across the four source encodings. That establishes byte identity for these outputs and this run; it does not establish how other inputs or converter versions behave.

The decoded 64×64 layer matched the 64×64 source pixel for pixel in all eight outputs. Across every decoded layer, this opaque artwork produced zero fully transparent pixels, zero partial-alpha pixels, and zero pixels with unequal RGB channels. The color check therefore found no hue shift in these grayscale outputs.

What the file sizes do—and do not—compare

The four pngtoicotool outputs were 14,762 bytes each. The four ConvertICO.com outputs were 370,070 bytes each. Those totals differ between converters, but they did not differ when only the PNG source color type changed within either converter. This test does not isolate why the two converters' output sizes differ.

Because the input had no transparent pixels, this matrix cannot answer whether RGB, RGBA, indexed transparency, or other alpha-bearing inputs retain transparency. It also covers one grayscale drawing, one configuration per site, and one conversion per input type.

Downloaded ICO results, decoded locally

Each source PNG was 64×64 and pixel-identical after decoding. Alpha counts are summed across all six decoded layers. `64×64 exact match` compares the same-size ICO layer against the decoded source.

All eight ICOs were downloaded and decoded locally with Pillow 12.3.0. The CSVs preserve the per-run hashes and per-layer measurements.

• Complete test evidence ZIP (inputs, downloaded ICOs, scripts, and measurements)
• Measurements CSV — one row per converter and PNG input
• Decoded frame CSV — one row per ICO layer

How this PNG to ICO comparison was run

1. 01
   Save one decoded image in four PNG types

   Use the included RGB, RGBA, indexed, and grayscale files. The fixture script verifies that all four decode to the same 64×64 opaque pixels.

2. 02
   Convert each file with the same settings

   Run each PNG once in each converter and save the downloaded ICO under its matching input name. Do not compare webpage size labels in place of downloaded bytes.

3. 03
   Decode every ICO layer

   Record the layer dimensions and ICO byte length, count fully transparent and partial-alpha pixels, and compare the 64×64 layer against the source pixels.