34  Raster Images

Figure 34.1: Common raster image file formats
PNG — Portable Network Graphics
  • Lossless Compression
  • Transparency support
  • 24-bit color depth
  • High detail and color depth make them better suited for photographs

PNG files are popular for web-sites given their small sizes, transparency ability and color depth. There are two main types.

PNG-8 — 8-bit color depth
  • Capable of displaying 256 colors
  • Small file sizes
  • Better suited for speed and simplicity in colors
GIF
definition
WEBP
definition
TIFF
definition
JPG/JPEG — Joint Photographic Experts Group
  • Lossy Compression

Non-progressive (Non-interlaced)

Progressive (Interlaced)

34.1 Dimensions

All possible colors represented in 16 bit RGB color (5 bits per color for red and blue and 6 for green).

Resolution
  • A measure of pixels in the display.
  • Screen resolution expressed as width x height
  • Image resolution expressed as megapixels (MP), i.e. millions of pixels.

e.g. A common monitor resolution of 1920 x 1080 means 1920 pixels across and 1080 pixels down. This fits the 16:9 aspect ratio typical of

refers to the number of pixels [an electronic image] contains, usually expressed as millions of pixels, or megapixels (MP)…The greater an image’s resolution, the better its quality.

DPI (dpi)
  • How many dots are present in a linear inch
  • A higher DPI allows for more detail
  • Prints typically use 300DPI
  • Screen typically use 72DPI