Bitmap

Definition updated by Sam Ingalls ← 

What is a bitmap? 

A bitmap is a file format or memory organization of rows and columns of bits (or pixels) that collectively display a graphical representation. Most graphic images contain thousands of bits. 

Also called a bit array, bitmap index, raster image, and sometimes pixmap, a bitmap is a domain and range of bits that present a rectangular visual made up of pixels. 

Pixels are larger squares made up of bits. Whether the pixel is black and white or color is the difference between 8 bits (B&W) and 24 bits (color). 

While the development of rasters dates back to the 1960s at Bell Labs, the bitmap format was pioneered by Microsoft in the 1980s to offer Windows customers device-independent images. 

Types of bitmap file formats

  • BMP: Bitmap
  • GIF: Graphics Interchange Format
  • JPEG: Joint Photographic Expert Group
  • EXIF: Exchangeable Image File
  • PNG: Portable Network Graphics 
  • TIFF: Tagged Image File Format

How do bitmaps work?

Bitmaps contain data that organize thousands of squares by position and assigned color into a single, viewable graphic image. 

The resolution of the bitmap is the density of these squares. A resolution of 800×600 for a computer monitor means the screen offers 800 pixels for 600 lines, or 480,000 pixels collectively for the display. The higher the number of pixels, the clearer (or more realistic) a graphic or digital photograph is. Fewer pixels display a blurrier representation.

Except for BMP, all other formats listed use a compression algorithm that makes the bitmaps smaller and easier to transfer over the internet. Because GIFs and JPEGs are suitable for web transfer, they frequently are seen in internet-enabled projects. 

Bitmaps and Data Compression 

Data compression is applied to bitmaps to alter files for storage and transfer. Highly compressed file formats result in a loss of pixels in the delivered version. The transferred image now appears more pixelated–more prominent, visible pixels–and less close to the original before sharing, altering, or photoshopping

The lower the compression, the more your bitmap will remain intact and similar to the original. 

Bitmaps vs. vector graphics

Vector graphics rely on mathematical formulas to define the shapes and colors of graphic depictions. Instead of pixels, vector graphics use bit formulas that make the format more scalable and alterable relative to bitmaps. 

Example: Vector graphics use scalable fonts that are compatible across device types. Bitmap fonts, by comparison, require a custom design with specific sizes and resolutions for every line of devices. 

Bitmaps’ lack of scalability has led to fluctuating usage over the years, yet they remain the primary file format for photographic images. 

Further Reading

Related Terms

Vangie Beal
Vangie Beal is a freelance business and technology writer covering Internet technologies and online business since the late '90s.

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