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Tool guide
This one runs against the usual compression instinct: a PNG is expanded into a 24-bit BMP where every pixel is three consecutive bytes, no palette and no compression. The file gets bigger — a 1000x1000 image lands at roughly 2.9 MB whatever it depicts — but that is exactly the BMP shop-floor terminals, label printers, old firmware, and Windows XP era utilities know how to read. The header is the standard 54-byte one, 96 DPI, rows written top-down. See also: convert a BMP file back to PNG, save a PNG as JPG without the alpha channel, set an exact width and height for the image.
Because the format has no compression at all. The size is width x height x 3 bytes, plus a 54-byte header, plus padding of each row to a multiple of four. A 1920x1080 screenshot lands near 5.9 MB regardless of content, while the same picture as PNG might be a hundred kilobytes. The bloat is the price of a format that old systems can read.
Transparency is lost: a 24-bit BMP stores R, G, and B only, with no room for alpha. Fully transparent pixels are written with zero colour values, which means they come out black. If you need white or a brand colour behind the subject, flatten the layers in an editor first — transparency cannot be recovered from the BMP afterwards.
A classic BITMAPINFOHEADER file: 24 bits per pixel, BGR channel order, no compression, 2835 pixels per metre, which is 96 DPI. Rows are stored top-down using a negative height in the header. Paint, old viewers, and most industrial readers open it with no extra settings.
Hardware and legacy software. Machine controllers, POS terminals, label printers, and lab or medical applications frequently accept nothing but uncompressed BMP, because their firmware predates widespread PNG support. Sometimes a vendor's own instructions for uploading a logo or splash screen name BMP outright, and then there is no choice.
The file picker is set to image/png and will not accept anything else. The workaround is easy: re-save the JPG or WebP as PNG with a neighbouring converter in the catalogue, then bring that file here. The extra hop costs no quality, since both steps are lossless.
No formal cap, but the entire pixel buffer is assembled in tab memory. Up to roughly 8000x8000 an ordinary computer copes; beyond that the tab may fail to allocate, since one such image is close to 200 MB of raw data. On a phone it is wise to stay within a couple of thousand pixels per side.
Before: logo.png, 320x240, 18 KB, background already filled with white
After: export.bmp, 320x240, 24-bit — 230,454 bytes: a 54-byte header plus 230,400 bytes of pixel data
Before: splash.png, 640x480, 96 KB
After: export.bmp, 640x480 — around 900 KB, readable by a loader that has no idea what PNG is
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