What is the BMP format?

1What is a BMP file?

BMP is Windows' native bitmap format. Its name says it all: it stores the image as a grid of pixels, where each pixel takes up a fixed number of bits. It was one of that system's first graphics formats, and programs like Paint have used it for decades.

Its great virtue is simplicity: any program can read and write it easily. Its great flaw is size: with no compression, a BMP takes up far more space than a JPG or PNG of the same image.

2How does a BMP work inside?

A BMP has a header that gives the width, height, color depth and, if needed, the palette, followed by the pixel data. Each row is padded to a multiple of four bytes. To work out how much a 24-bit image weighs, just multiply: width by height by three bytes, plus small padding margins. A 4,000 by 3,000 pixel photo will take up about 36 megabytes.

Some variants allow simple run-length compression (RLE) in 4- or 8-bit images, and there are versions with an alpha channel, but support is uneven. That is why, in practice, a BMP is almost always a direct dump of pixels.

3Advantages and limitations of BMP

Advantages: no quality loss, very simple, and it opens in almost any Windows viewer. It is also useful in programming projects or electronic devices that need to read images without compression libraries. Limitations: it is heavy, uncommon on the web, impractical for email or social networks, has poor transparency support and lacks modern metadata such as EXIF.

If your BMP comes from an old screenshot, a scanner or a drawing program, it is best to convert it before sharing. You will see the file get smaller with no visible loss if you use PNG.

4BMP vs. PNG, JPG and TIFF

PNG holds the same thing as a true-color BMP, but compressed without loss, so it is much smaller and supports transparency. JPG shrinks the file even more for photographs in exchange for a small loss of quality. TIFF is another lossless format, more flexible, used in scanning and printing.

Practical rule: to archive without losing quality, PNG or TIFF; to share photos, JPG; for graphics or screenshots, PNG. Keep BMP only if a program or device requires it.

5Common BMP problems

The main one is file size: it can be impossible to attach a BMP to an email or upload it to a portal. “Compress image” and “Resize image” solve it by converting it to an efficient format and adjusting its dimensions. Another problem is that some sites or apps don't accept BMP; converting it to JPG or PNG fixes that.

If you need to include a BMP in a document, “Images to PDF” places it on a page and the resulting PDF will be much lighter than the original. In that case, check that the image doesn't lose sharpness when scaled.

6Practical tips for BMP images

Before converting, decide what you need: if the image is a graphic with few colors, PNG will be excellent and very small; if it is a photo, a high-quality JPG offers big savings. Keep the original BMP if it's the only copy you have of an important capture, and work on a copy.

As with the other Rayo PDF GO tools, the conversion happens on your device, without sending the file to any server, which is convenient if the BMP contains sensitive information.

It is also worth knowing that when you save a BMP again as PNG, there is no loss at all, because both keep the pixels exactly as they are. That is the safest conversion when you need to cut file size without touching quality, and that's why it is usually the first step before any other touch-up.

7How to get the most out of BMP in Rayo PDF GO

The typical case is a huge BMP that can't be sent. Reduce its dimensions with “Resize image” and save it again with “Compress image” to get a much lighter file. If you need several images in one document, “Images to PDF” groups them and the result works in any viewer.

When the BMP comes from a scanner or an old program, check that the dimensions and sharpness are sufficient before converting, because converting to a smaller format doesn't bring back detail that was already missing. And if the image contains personal data, process it on your device, just as these tools do.