> I thought if you use compression, you'll always lose at least a small amount of data. No, the terms "lossless" and "lossy" are attached to different compress

> I thought if you use compression, you'll always lose at least a small amount of data. No, the terms "lossless" and "lossy" are attached to different compression methods to indicate whether they do or don't discard data. Lossless compression methods like PNG, FLAC, ZIP, RAR, etc. will output the exact same input. Lossy compression methods, which discard some of the input data, include JPEG, MP3, AAC, MPEG-4 video (e.g. AVC, HEVC), and many more. As PNG is lossless, you can convert your BMPs into PNGs (which will make it far smaller) and back to BMPs, without a single pixel changing in any way. However, note that some PNG "optimizers" may introduce loss with some settings, like reducing the color space, but that's incidental to the format... You can reduce the resolution or color space of a BMP image to reduce its size as well.