# BMP to PNG reproducible samples

Experiment: 2026-10-29. Original synthetic Windows BMPs, eight valid and four diagnostic inputs. Run generate-fixtures.py with Python and Pillow; input bytes are deterministic. Open https://filepetal.com/bmp-to-png/, choose a BMP, convert and save the actual PNG. Compare dimensions, bytes and SHA-256 in verification.json; browser encoders may differ. Use an independent PNG reader to check the four alpha bands, row-order pair and palette. Identical BMP pixel arrays in the two 32-bit fixtures have different header interpretations; V4 explicitly supplies alpha masks, ordinary BI_RGB does not. Transparent hidden RGB can change during canvas use. No universal metadata or color-profile preservation claim. RLE, embedded JPEG/PNG, physical phones and competing conversion outputs not tested. The new preview does not alter the old conversion algorithm or remove backgrounds. Keep source files.