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Bitmaps are enormous because they store every pixel raw. PNG stores the identical pixels and compresses them losslessly.
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A BMP file applies essentially no compression, so a 1920×1080 bitmap occupies about 6 MB regardless of what it depicts. PNG encodes the exact same pixels with lossless compression and typically lands 70–90% smaller — a genuinely free win, since not a single pixel changes. That makes this the correct conversion for anything you inherited from legacy Windows software, scanning utilities, older scientific instruments or embedded systems that still emit BMP. Screenshots, diagrams and flat-colour graphics compress hardest; photographic bitmaps gain less but still shrink substantially. PNG also travels better: it is supported everywhere on the web, whereas BMP is rarely served online at all. There is no quality setting to weigh up, because there is no quality decision to make.
None whatsoever. PNG compression is lossless, so the output is pixel-identical to the bitmap.
Typically 70–90% smaller. Screenshots and flat graphics compress the hardest; photographic content gains somewhat less.
BMP stores raw pixel data with essentially no compression — roughly three bytes per pixel regardless of image content.
PNG has been universally supported since the late 1990s, so anything that opens a BMP will almost certainly open a PNG.
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