Ternary Image

Use the Grid and Image > Display on Map > Ternary Image menu option (GRIDIMGT GX) to place a ternary colour image on the map. This functionality is typically used to create radiometric maps. A ternary colour image maps each of the primary colours to the amplitudes of a single input grid. You can choose the cyan-magenta-yellow model (CMY) or the red-green-blue model (RGB).

Ternary Image dialog options

Colour model

Select from one of the colour models available:  "CMY", "RGB", "CMY inverted", or "RGB inverted"

Script Parameter: GRIDIMGT.MODEL

Colouring method

Specify the colour zoning method (colour stretch) for rendering colour distributions. Select one of the options below:

  • Histogram equalization (default zoning method)

  • Normal distribution

  • Linear

  • Log-linear

Check the Colour Tool topic to learn about the transform methods for zoning data, and how you can interactively modify the colour grid zones using the available methods.

Script Parameter: GRIDIMGT.ZONE

Red-Cyan grid

Select the colour grid to control the red or cyan colour.

Script Parameter: GRIDIMGT.GRIDRC

Green-Magenta grid

Select the colour grid to control the green or magenta colour.

Script Parameter: GRIDIMGT.GRIDGM

Blue-Yellow grid

Select the colour grid to control the blue or yellow colour.

Script Parameter: GRIDIMGT.GRIDBY

Shading grid

Optionally, select the grid that controls the shading colour. This is used when four grids need to be combined.

Script Parameter: GRIDIMGT.GRIDX

Shading grid colouring method

Similar to the colouring method, this is applied only to the shading grid.

Script Parameter: GRIDIMGT.ZONEX

Application Notes

Click the New Map button to display a grid on a new map. Click the Current Map button to display the grid on the current map. (For a script file, set 'Script Parameter: GRIDIMGT.NEW' to 1 to create a new map or 0 to use the current map)

Selecting Colour Tables for Ternary Images

The CMY model will use the colour tables: w-c.tbl, w-m.tbl and w-y.tbl. The RGB model will use the colour tables: k-r.tbl, k-g.tbl and k-b.tbl. These tables vary from white (CMY) or black (RGB) for lows in the grid to the indicated primary colour for highs in the grid.

The CMY inverted model will use the colour tables: c-w.tbl, m-w.tbl and y-w.tbl. The RGB inverted model will use the colour tables: r-k.tbl, g-k.tbl and b-k.tbl. These tables vary from the indicated primary colour for lows to white (CMY inverted) or black (RGB inverted) for highs.

The shading grid will use either the lgrey.tbl (for CMY models) or the rgbgrey.tbl (for RGB models). These tables produce darker/lighter colour changes in the image.

When using ER Mapper ternary colour images, the band numbers should be specified for each colour grid.

As an example, for an ER Mapper file named "Weshade.ers(ERM)", the following should be entered in the three colour bands:

Red-Cyan grid Weshade.ers(ERM;band=0)

Green-Magenta grid Weshade.ers(ERM;band=1)

Blue-Yellow grid Weshade.ers(ERM;band=2)