Raster Graphics

Raster graphics (Raster Logos) are images that are defined in terms of a generally rectangular grid of pixels, or picture elements. Each pixel is one small square of colour, which, when combined with other pixels side by side, merge together to form one solid image to the eye.

Raster formats:
There have been a number of formats developed over the years to store raster graphics. Some of the most popular formats are discussed below, each with their advantages and disadvantages.

BMP - Bitmap Graphics (Avoid wherever possible)

• Easy to create with the built-in Windows Paint program.
• Long history, therefore good, universal support.
  
• No compression means the format is lossless.
• Creates huge files since no file compression is used.
• No transparency.

GIF - Graphics Interchange Format (Good for the web, on images of less than 256 colours, for example simple geometric shapes e.g. bullets for lists)

• Creates small files as good compression is used.
  
• Universally supported across platforms.
  
• Transparency supported.
  
• Animation supported.
  
• Palette of colours limited to 256 per image.
• Transparency is only 1-bit, therefore no translucency.

JPG - Joint Photographic Expert Group (Good for the web, for images like photographs where colour depth is important but lossless formats produce large file sizes)

• Lossy compression format produces relatively small files.
  
• Universally supported across platforms.
  
• Artifacts visible at high compression rates.
  
• No transparency.

PNG - Portable Network Graphics (Great for the web, but be careful if using transparency. Good trade-off of quality and compression)

• Both lossy and lossless compression available.
  
• Both 1-bit and full alpha channel transparency available.
  
• Small file sizes produced.
  
• Poor support in some web browsers for full channel transparency.
• Compression not as great as lossy formats.