Convert BMP to PNG
Drop in your BMP files and download PNGs. Every pixel comes across unchanged, and the files are converted here on your device, never sent to a server.
Converted files appear here.
How to use it#
- Drop your BMP or DIB files onto the box above, or click it to pick them.
- Check the size of each PNG in its row.
- Download each PNG, or take them all at once.
Where BMP files come from#
BMP is the bitmap format Windows has used since its early versions. Paint saves to it, older Windows programs export it, many scanners and their software default to it, and some screenshot and capture tools write it. Most BMP files store every pixel as it is, with no compression, which is why a folder of them fills a disk and an upload form turns them away.
PNG stores the same pixels with lossless compression, so nothing is lost and the file shrinks. Every browser, phone, and image editor opens a PNG, and websites that turn a BMP away accept one.
What comes across, and what it costs#
Every opaque pixel comes across unchanged. PNG is lossless, so there is no quality to choose and the colours are the BMP's own. A 256 colour BMP comes out as a full colour PNG with the same colours. A 32-bit BMP that declares an alpha channel keeps its transparency, and the preview in each row shows the see-through parts.
How much smaller the PNG gets depends on the picture. In testing, an 800 by 600 drawing in flat colours went from 1.4 MB to 17 KB, and a 1440 by 900 screenshot of text and panels from 3.7 MB to 399 KB. A 1920 by 1080 photo only went from 5.9 MB to 4.1 MB, because the grain in every pixel of a photo or a scan is what lossless compression cannot squeeze. The size of each result is shown in its row, measured on the file this page has just written.
When JPG is the better choice#
For a photograph, or a scan of one, a JPG is several times smaller than the PNG and looks the same at normal viewing size, because JPEG throws away detail the eye does not notice in a photo. The 1920 by 1080 photo above was 4.1 MB as a PNG and 509 KB as a JPG at 92% quality. If the file only has to be small enough to email or upload, use BMP to JPG instead.
Keep PNG for anything with text, sharp lines, or flat colour, such as a screenshot or a diagram, where JPEG leaves faint smudges around edges. Keep it too for a picture you will edit again, since every JPG save loses a little more, while a PNG can be saved as often as you like.
Frequently asked questions#
Are my files uploaded anywhere?
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No. Your browser reads the BMP and writes the PNG on your own device. Nothing is sent to a server.
Is BMP to PNG lossless?
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Yes. PNG stores every pixel exactly, so a BMP with no transparency, which is nearly every BMP, comes out identical down to the last pixel. That is why there is no quality slider on this page.
Does it read .dib files?
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Yes. A .dib is a device-independent bitmap, the same format as a BMP under another name, and it converts the same way.
Is the transparency in a 32-bit BMP kept?
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Yes, when the BMP declares an alpha channel, as the newer BMP headers that image editors write for transparent files do. The see-through parts show in the preview in each row. A plain 32-bit BMP marks its fourth byte as unused, so the browser reads it as fully opaque, and so does most other software. A fully see-through pixel keeps no colour of its own in the PNG, and a partly see-through one can move by a single step in a colour value, since the browser works with transparent pixels that way. Every opaque pixel comes across exactly.
Why is my PNG not much smaller than the BMP?
#
A photo or a scan has fine grain in every pixel that lossless compression cannot shrink much, and a few BMPs are already compressed. For a photo that just needs to be small, BMP to JPG makes a far smaller file.