BMP (Bitmap Image File)

GISBox is a one-stop 3D GIS data editing, conversion and publishing platform that supports editing in multiple GIS formats such as OSGB/GEOTIFF/RVT, converting to 3DTiles/Terrain and publishing.

Introduction

BMP file (bitmap file, extension: .bmp) is a file format for storing bitmap images, developed by Microsoft. It is widely used as a standard image format in Windows environment, mainly used to process uncompressed raster images. Since BMP files store each pixel data of the image as it is, they can display high-quality and lossless images, but the file size is often large.

File Structure

Main specifications of BMP:

Color depth:

1 bit (black and white)
4 bits (16 colors)
8 bits (256 colors)
24 bits (full color, 16.77 million colors)
32 bits (full color with alpha channel)

Compression format:

No compression (standard format)
Support RLE (Run Length Encoding) compression method (only for 4 or 8 bits)

Byte order:

Use little endian byte order to store data and follow the little endian format.

Scan line padding:

Each line of data is padded to a multiple of 4 bytes.

Pros

Lossless image: BMP uses a non-compressed format, so the image quality will not be reduced and high-precision details can be maintained.
Easy to edit: The data structure is simple, and the program operation and editing are convenient.
Strong compatibility: Windows system natively supports BMP format, which is very convenient to display and edit, and most graphics tools support it.
Flexible color: Supports multiple color depths from monochrome to 16.77 million colors.

Cons

Large file size: Due to the use of uncompressed storage, the file size is often very large, especially for color images of 24 bits or above.
Low compression efficiency: Although RLE compression is supported, the effect is limited and the compression rate is much lower than JPEG or PNG.
No support for transparency: 24-bit format does not support alpha channel (transparency information), so transparent images cannot be saved. Although 32-bit format supports transparency, not all software can recognize it.
**Not suitable for web applications: **The file size is large and is not suitable for web page display or online transmission.

Application Scenario

BMP is commonly used in the printing industry and DTP (desktop publishing) field due to its lossless image characteristics. It is especially suitable for saving and editing high-resolution logos, icons and other images. In Windows applications, BMP is often used for interface elements such as icons and startup screens. Since the DIB format can maintain consistent display effects on different devices, BMP is suitable for software GUI design. BMP is also commonly used in medical imaging (such as CT scans or microscope images) and scientific visualization because of its non-compression characteristics that can retain high-resolution data. In addition, BMP is also used to store map tiles or elevation data. This format can save accurate geographic information without loss.