Images that already have 256 or fewer colors, whether as a result being converted to grayscale or being from a format with a palette, are being dithered unnecessarily on save. I believe this is a regression in 4.2.16. This is particularly concerning because it makes Auto-detect lossy for these PNGs.   The following PNG-8 and GIF were generated externally:    The files after being opened and saved with default settings in paint.net:    There is now noticeable dithering