BMP から JPG への変換ツール — Windows ビットマップを JPG に変換

The Quality slider runs from 20 to 100; keep it near 90 (the default) for photos where you want the file size cut dramatically with almost no visible loss versus the uncompressed BMP. Drop it to 60–75 for screenshots or web thumbnails where a smaller file matters more than pixel-perfect detail.

JPEG itself can't store an alpha channel, so the tool always includes a Background fill color swatch — white by default — that gets applied to any transparent pixels before the file is flattened. It matters most for 32-bit BMPs that do carry alpha data; change the swatch if you need the fill to match a specific page or brand background instead of white.

Yes, using Batch mode. Toggle from Single file to Batch, drop in multiple BMP files, and the same Quality and Background fill settings you've set are applied to every file, which are then bundled into one ZIP — this is a Premium feature, so free accounts convert one BMP at a time.

Since BMP screenshots are already opaque and mostly flat color, set Quality to around 70–80 (plenty of fidelity for UI captures) and leave Background fill on white, then switch to Batch mode to convert the whole folder into a single downloadable ZIP in one pass instead of repeating the conversion file by file.