When PNG to BMP turns PNG into BMP
An old Windows program, a machine tool, or a textbook CD only opens BMP.
What PNG to BMP changes in the picture
The PNG is written as an uncompressed bitmap. Transparency becomes a solid background. The file gets much larger.
Do not send BMP by email if PNG was accepted. Keep the PNG, which is the better copy.
When PNG to BMP is the right page
PNG to BMP sits on this site because PNG and BMP are not interchangeable, even when they look similar in a file list. An old Windows program, a machine tool, or a textbook CD only opens BMP. Use PNG when a logo must stay crisp or when the background must stay transparent. Machine tools, textbook CDs, and old Windows programs sometimes open only BMP.
The PNG is written as an uncompressed bitmap. Transparency becomes a solid background. The file gets much larger.
What you give up by leaving PNG
PNG keeps sharp edges and transparency. Screenshots, logos, and diagrams belong in PNG. Photographs are usually much larger as PNG than as JPG, with little visual gain.
Keep the PNG master of a logo. Export JPG only for the places that refuse PNG.
What you gain, and do not gain, with BMP
The download has to be BMP, because that is the format the next step named. Machine tools, textbook CDs, and old Windows programs sometimes open only BMP. Those old programs get a file they understand.
BMP does not look better than the PNG or JPG you started with. It is only less compressed.
A test that matches the real file
Start from the question the other software asked. If it asked for BMP, PNG to BMP is the matching page. If it asked for something else, switch tools instead of hoping a similar extension will pass. An old Windows program, a machine tool, or a textbook CD only opens BMP. The PNG is written as an uncompressed bitmap. Transparency becomes a solid background. The file gets much larger. The limit is the part people skip, and it is the part that decides whether the download is usable. Do not send BMP by email if PNG was accepted. Keep the PNG, which is the better copy. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Check three things in the download: it opens, the PNG material you cared about is still there, and the file size or the layout is what the form described. A new extension alone is not those three things. If a portal, a teacher, or a client rejects the file, send them the original PNG as well when you are allowed to. PNG to BMP is a convenience copy. It is not a new master. Photos fail uploads for three separate reasons: the format name, the pixel size, and the kilobyte size. PNG to BMP only does the PNG to BMP step. If the form also prints a pixel size or a 20 KB or 50 KB cap, do that step with the matching tool, starting from the original each time. A second lossy save will not recover detail.
Here is the decision for PNG to BMP. You start with PNG and you stop when a real program accepts BMP. Text in a screenshot stays sharper than it does in a heavy JPG. Transparency is lost, and the file grows a lot compared with PNG. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Do not send BMP by email if PNG was accepted. Keep the PNG, which is the better copy.
A related step, if you still need one, is BMP to PNG.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.