Convert Image to BMP

Nobody chooses BMP. Something demanded it.

Worth saying plainly, because it shapes everything else.

BMP has no advantages over the modern formats for any ordinary purpose. It is uncompressed, so files are enormous; it has no metadata to speak of; and it is supported everywhere mainly because it is very old and very simple.

So the reason to make one is always external. In practice that means:

Legacy Windows software that was written when BMP was the obvious choice and never updated — line-of-business applications, older database front ends, in-house tools.

Embedded and industrial systems. Machine control panels, test equipment, instrument displays, older point-of-sale terminals and kiosk software frequently accept BMP and nothing else, because a BMP needs no decoding library at all — the pixels are simply there in order.

Game modding and older game engines, where textures, sprites and interface elements are often expected as BMP.

Some print drivers, label printers and sign-cutting software.

Firmware and microcontroller projects, for the same reason as embedded systems: reading a BMP takes a few lines of code and no dependencies.

And if nothing has demanded it, use PNG instead. PNG is also lossless, it keeps transparency, it is a fraction of the size, and everything made in the last twenty-five years reads it. Convert Image Format will produce one.

The files are very large, and here is the arithmetic

The output is 24-bit uncompressed, which means exactly three bytes per pixel plus a tiny header. No compression of any kind.

So a 12-megapixel phone photo becomes about 36 MB. A 24-megapixel camera photo becomes about 72 MB. A 1920 by 1080 screenshot becomes about 6 MB. A small 500 by 500 icon becomes about 750 KB.

Compared with a JPEG of the same photograph at two or three megabytes, that is a fifteen- to twenty-fold increase, and it is entirely predictable: multiply width by height by three.

Two practical consequences. Resize before converting, not after — if the destination only needs a 640 by 480 image, Resize Image first turns a 36 MB conversion into a 900 KB one. And if the receiving system has a file size limit, work out the arithmetic before you convert rather than after.

Transparency is lost

The one thing that catches people, and it is inherent to the format as written here.

24-bit BMP has no alpha channel. Three bytes per pixel means red, green and blue, with nothing left for transparency. So a transparent PNG converted to BMP comes back with those areas filled — and a logo that was designed to sit on any background arrives as a logo on a solid rectangle.

If that is a problem, you have two options. Flatten it deliberately first, onto whatever colour it will sit on, so at least you control the result rather than discovering it. Or use Convert Image to TIFF instead, which is also uncompressed but does carry an alpha channel — if the receiving software will take TIFF, it is the better of the two formats in every respect.

What you get, and why there is no fallback

One detail worth knowing, because it is unusual among format converters.

Most in-browser converters ask the browser to encode the format, which means the result depends on what your browser supports and can quietly come back as something else. This tool writes the BMP file itself — the standard header followed by the pixel data, assembled byte by byte.

The practical upshot is that there is no feature detection, no fallback and nothing that can silently degrade. You asked for a BMP and you get a BMP, in every browser, every time. The output is the plain 24-bit form that legacy software expects, rather than one of the format's more exotic variants that older readers often choke on.

Add as many images as you like — they convert in one pass and come back as a ZIP, keeping the original filenames with the extension changed. Everything happens on your own device, with no upload, no watermark and no account.

Related tools

Convert Image to TIFF is the other uncompressed format and the better one — it keeps transparency, and it is what print and archive workflows actually ask for. Convert Image Format produces PNG, which is what you want if nothing specifically demanded BMP. Resize Image is worth running first, since the file size is exactly proportional to the pixel count.