Bitmap images; bitmap versus vector

Bitmap images

A bitmap (raster) image is a picture made of a rectangular grid of tiny dots called pixels. Each pixel stores its own colour value (1 bit for black and white, 8 bits for 256 colours or grey, 24 bits for true colour). The image is defined by its width and height in pixels and its colour depth, for example 800 x 600 at 24 bits needs 800 x 600 x 3 = 1,440,000 bytes uncompressed. Photographs from cameras and scanners are bitmaps. Formats: BMP, JPEG, GIF, PNG, TIFF. Software: Photoshop, GIMP, Paint.

 pixel grid (each cell = one colour value)
 +--+--+--+--+
 |12|14|90|91|
 +--+--+--+--+
 |11|80|95|92|
 +--+--+--+--+

Advantages of bitmap over vector

1. Photo-realism. It can show continuous tones, shading and subtle colour changes of real scenes; vector graphics look flat or artificial for photographs.
2. Direct capture. Cameras and scanners produce bitmaps directly, no conversion needed.
3. Pixel-level editing. Any individual pixel can be changed, allowing retouching, filters and special effects.
4. Simple display. Rendering only maps pixels to the screen, so complex pictures display quickly, regardless of the complexity of the scene.
5. Wide support. Every browser, device and program can show common bitmap formats.

Disadvantages of bitmap compared with vector

1. Large file size. Size grows with resolution and colour depth, and does not depend on image content; vector size depends on number of objects and is small for simple drawings.
2. Resolution dependent. Enlarging a bitmap makes it blocky (pixelation) and blurry, while vector images scale to any size without loss.
3. Hard to edit objects. A shape cannot be moved or resized as an object; the pixels must be selected and repainted.
4. Poor for line art and text. Logos, diagrams and fonts look jagged at low resolution.
5. Needs compression for storage and web transfer, and lossy compression reduces quality.
6. Printing at different sizes needs high-resolution originals.