How to create a color composite

A color composite is created by combining three raster images (bands/maps). One map is displayed in shades of red, one in shades of green and one in shades of blue. Putting the three bands together in one color composite can give a better visual impression of the reality on the ground, than displaying one band at a time.

There are three types of color composites: natural color composites, pseudo natural color composites and false color composites. Natural color composites are made of the green, blue and red part of the spectrum. This results in an image with realistic colors. A pseudo color composite is created with other parts of the spectrum, but the result has natural looking colors. In false color composites the colors in the image are not the same as in reality: for instance, healthy vegetation is red and urban areas are blue.

In ILWIS, there are two ways in which you can display or create a color composite:

by showing a map list as a color composite; the resulting color composite is displayed in a map window (interactive color composite), and
by using the Color composite operation; the resulting color composite is stored as a raster map on disk (permanent color composite).

Interactive color composites:

An interactive color composite can be created when your graphics board is configured to use more than 256 colors, for instance High Color 16-bit, or True Color 24-bit (see Display Settings in Windows' Control Panel).

To obtain an interactive color composite:

from the Operations menu in the Main Window, choose Visualization, Show Map List as Color Composite,
in the Operation-tree, open the Visualization item, open the Show Map List item, and double-click the Color Composite item, or
in the Operation-list, double-click the ColorComp item.

When you use one of these methods, first the Show Map List as Color Composite dialog box will appear: you have to select a map list. After you selected a map list, the Display Options Map List as Color Composite dialog box will appear, see below.

To obtain an interactive color composite, you can also:

open a map list by double-clicking it in a Catalog, then click the Show as Color Composite button in the map list editor;
use the right mouse button on a map list in a Catalog and select Visualization, as Color Composite from the context-sensitive menu.

The Display Options - Map List as Color Composite dialog box will appear:

select three raster maps (domain Image or a value domain) from the map list, which should be displayed in Red, Green and Blue;
if you wish you can also display bands in Yellow, Magenta, Cyan (YMC) or as Hue, Saturation, Intensity (HSI);
for each map, specify the stretch range.

The interactive color composite will be displayed in a map window.

You can easily change intervals, select other bands, etc. by changing the display options of the map list:

double-click the map list in the Layer Management pane of the map window,
open the Layers menu in the map window, choose Display Options and select the map list, or
use the right mouse button in the map window and select the map list from the context-sensitive menu.

To save an interactive color composite, save the contents of the map window as a map view. Open the File menu in the map window and choose the Save View command.

Permanent color composites:

The output of the Color composite operation is stored as a raster map on disk.

To create a permanent color composite:

from the Operations menu in the Main Window, choose Image Processing, Color Composite, or
in the Operation-tree, open the Image Processing item, and double-click the ColorComp operation, or
in the Operation-list, double-click the ColorComp operation, or
drag an image from a Catalog to the ColorComp operation in the Operation-tree or Operation-list.

The Color Composite dialog box appears:

select three raster maps (only domain Image allowed) which should be displayed in Red, Green and Blue.
specify the type of color composite which you want to create:

standard color composite: choose between linear stretching (values or percentage intervals) and histogram equalization,
dynamic color composite: specify the number of output colors,
24-bit color composite (when your graphics board is configured to use more than 256 colors): choose between linear stretching (values or percentage intervals), histogram equalization or use instead of images, Hue, Saturation and Intensity bands as input.