Creating raster pyramid – recommended output format

Raster loader conversion output can be set to lossless PNG or lossy JPG.

  • JPG – is designed for compressing either full-color or gray-scale images of natural, real-world scenes. It is best suited for continuous tone images like photographs – not so well on sharp-edged or flat-color art like lettering, simple cartoons, or line drawings. JPG is designed to exploit certain properties of our eyes, namely, that we are more sensitive to slow changes of brightness and color than we are to rapid changes over a short distance.
  • PNG – is lossless compression method, well suited for images containg areas of even colour or sharp-edged geometries. It is designed for image data typically dominated by hard, high-contrast transitions, and regular structures (without noise).

To gain best final effect and get optimum raster pyramid from your input raster images take a look at following recommendation:

  • scanned vector maps (true colour or shades of grey) – inappropriate for PNG, recommended conversion to JPG format. It is characterised by uneven background colour.
  • scanned vector maps (monochromatic) – suitable for PNG format – the background areas should be uniform in colour (preferably white) while all the drawings should be just black lines.
  • rendered vector maps (most often Ordnance Survey raster maps) – suitable for PNG format
  • aerial imagery – recommended conversion to JPG format