BMP is an old format that stores every pixel without compression. Some older Windows programs, embedded displays, game tools and scripts only accept BMP, and converting a JPG is the way to feed them a photo.
Expect a large file. A BMP takes about three bytes per pixel, so a 12-megapixel photo becomes roughly 36 MB, even when the JPG was a few megabytes. Converting does not bring back any detail the JPG already discarded: the BMP simply holds the decoded pixels as they are. JPG has no transparency, so there is nothing to lose there, and there is no quality setting, because BMP does not compress.
The pixel dimensions never change, each file keeps its name with only the extension swapped, and no metadata or watermark is added. Everything runs in your browser, so your images are never uploaded.
Because BMP is so simple, it is easy for other programs to read. That makes it handy for test images, scripts that read raw pixels, and tools that predate JPG. Convert one file first to check that your program accepts it, then convert the rest in one go and download them as a ZIP.
Tip: use BMP only where it is required. For everything else, the JPG is the better file to keep and share.
JPG compresses photographs heavily, and BMP does not compress at all. Every pixel is stored in full, about three bytes each.
No. The BMP holds the pixels exactly as the JPG decodes them, including any softness or artefacts. It just cannot lose anything more.
No. BMP is uncompressed, so there is nothing to adjust.
A standard 24-bit uncompressed BMP, which almost every program that reads BMP can open.
Yes. Add them all, convert once and download a single ZIP. Only the extension changes. A file named holiday.jpg becomes holiday.bmp.
No. The conversion happens in your browser and the files never leave your device.