BMP to PNG Converter — Same Pixels, a Fraction of the Size

BMP, short for bitmap, is the image format Windows has used since its early versions. It is about as simple as an image file can be: a short description of the picture followed by the colour of every pixel, one after another.

Header, Palette, Pixels

A BMP starts with a 14-byte file header and an information header that records the width, height and colour depth. Images with 256 colours or fewer then list their colours in a palette. After that come the pixels, row by row, usually starting from the bottom row of the picture and working up.

Bit Depth

The bit depth decides how many colours fit in a pixel. 1-bit bitmaps are black and white, 4-bit ones have 16 colours, 8-bit ones 256, and 24-bit files hold 16.7 million. A 32-bit BMP adds a fourth byte, which some programs use for transparency and others leave as padding.

Why BMP Is Still Around

Because it is so simple, BMP is easy for any program or device to write. Old games, Windows utilities, sprite editors and embedded displays still produce it, which is why BMP to PNG remains a common job.

Most BMPs are not compressed at all. The file size is simply width × height × bytes per pixel, plus a little padding.

The Arithmetic

A full-HD screenshot is 1920 × 1080 pixels. At 24 bits, that is 3 bytes per pixel, or about 6.2 MB, no matter whether the screen showed a busy photo or a blank white page. The same screenshot as PNG is often a few hundred kilobytes.

Row Padding

Each row of pixels is padded to a multiple of 4 bytes. It adds little to large images but shows how literally BMP stores the picture: byte for byte, with no attempt to save space.

Compressed BMPs exist, but rarely

The format does allow simple run-length compression for 4- and 8-bit images, which helps with large flat areas. Most programs skip it, and 24-bit bitmaps cannot use it at all.

Converting BMP to PNG removes that waste without touching a single pixel, which is why the PNG is often 80–95% smaller. The result list shows the exact saving for each file.

PNG compresses without throwing anything away. It looks for repetition, such as a row of identical pixels or a pattern that repeats, and stores it once.

Same Pixels, Smaller File

A BMP converted to PNG decodes to exactly the same pixels as the original bitmap. Colours, edges and text stay identical, which matters for screenshots, user interface mock-ups and pixel art where a single changed pixel is visible.

Palette Bitmaps Stay Palette Images

1-, 4- and 8-bit bitmaps use a palette of at most 256 colours. This converter saves them as palette PNGs too, one byte per pixel, rather than expanding them to full colour. That keeps the PNG as small as possible.

What about 32-bit bitmaps?

When a 32-bit BMP declares a transparency channel and your browser reads it, the PNG keeps the transparency. Many programs, however, write the fourth byte as plain padding, and then the bitmap is simply opaque.

BMP files from games, emulators and old Windows toolbars often show a shocking pink background. That is deliberate: before formats with transparency were common, developers painted the see-through area in pure magenta, a colour almost never used in artwork, and told the program to skip it.

One Click to a Transparent PNG

Tick "Make magenta (#FF00FF) transparent" and every pixel of exactly that colour becomes transparent in the PNG. The result list counts how many pixels were changed, so you can see it worked.

Exact match only

Only pure #FF00FF is replaced. Shades that are almost magenta, such as anti-aliased edges, stay as they are, so the option never eats into the artwork itself.

A few games used a different key colour, such as pure green or black. This option handles magenta, by far the most common choice; other keys are better removed in an image editor.

PNG is the natural replacement for BMP whenever the image has sharp edges, flat colours or text.

Ideal for PNG

• Screenshots and app windows from older Windows tools.
• Icons, cursors and pixel art.
• Diagrams, charts and logos.
• Sprite sheets and game textures, with the magenta option where needed.

When JPG Is Better

Photos and scanned pictures contain fine noise that lossless compression cannot shrink much. For those, BMP to JPG produces a file many times smaller with no visible difference.

Keeping a BMP for a reason

Some devices, boot screens and microcontroller displays only accept BMP input. Keep the original for those and use the PNG everywhere else.

To squeeze the PNG further, run it through compress PNG. For websites, PNG to WebP gives an even smaller file with transparency intact, and resize image sets exact dimensions.

For photos, use BMP to JPG instead. Every other format pair is listed in the image converter.