You can read and draw raster pictures like any other files. If you want raster pictures in the same scale as vector pictures or other raster pictures, you first have to change coordinates.
Raster pictures can be used as background pictures e.g. for digitizing and calculating coordinates. There can be many raster pictures on the screen at one time. Raster pictures are always drawn before vector pictures, even if given in the file element list after vector pictures.
Raster picture can be set transparent. In practice this means, that drawing of white pixels is skipped. Transparent raster images are always drawn above other raster files regardless their order in the element list. Transparency works also when writing picture file to raster file, but slows down file creation noticeably.
If you use the raster picture for digitizing and calculating coordinates, note the following points:
- the program cannot rotate the raster picture during digitizing. If the picture you are using to digitize the coordinates from is not orientated in the same direction as the coordinate axis, you have turn the axis of the points you are calculating at a later stage.
- you can zoom the raster picture until one pixel fills the whole screen. The points may be focused, but you have to remember, that focusing affects scanning density.