Symbolize a single band image with a multi-color ramp

Summary

This article provides a script that applies a multi-color ramp to single-band image.

Procedure

1. Open a new script.
   
   
   A. Activate the Project window.
   B. Click the Scripts icon.
   C. Click New.
   
   
2. Paste the following script into the script window:
   
   

   Code:
   '-- The following script applies a "red to blue to white"
   '-- color ramp to a single band image legend.
   '-- It assumes that the active doc is a view and that
   '-- one and only one theme is active in that view and that the 
   ' active theme is an image theme with a single band image legend. 
   
   theView = av.GetActiveDoc 
   theTheme = theView.GetActiveThemes.Get(0) 
   theLegend = theTheme.GetLegend 
   
   '-- Get the color map from the image legend. This is easiest.
   '-- You can create a new color map using ColorMap.MakeRandom, 
   '-- ColorMap.MakeNominal, or any of the ColorMap.Make* request.
   '-- It doesn't really matter which one you use as long as
   '-- you set the size to 256. If you make a new color map 
   '-- then before theTheme.UpdateLegend you need to do 
   '-- theLegend.SetColorMap(newColorMap) 
   
   theColorMap = theLegend.GetColorMap 
   
   '-- Create a red to blue color map and a blue to white
   '-- color map each with 128 colors 
   
   redBlueColorMap = ColorMap.MakeRamp(128,Color.GetRed,Color.GetBlue) 
   blueWhiteColorMap = ColorMap.MakeRamp(128,Color.GetBlue,Color.GetWhite) 
   
   '-- Use the two new 128 color maps to apply colors
   '-- to the original 256 color map or a new 256 color map. 
   
   for each i in 0..127 
   theColorMap.Set(i,redBlueColorMap.Get(i)) 
   end 
   for each i in 128..255 
   theColorMap.Set(i,blueWhiteColorMap.Get(i-128)) 
   end 
   
   '-- Update the legend and redraw theme. 
   
   theTheme.UpdateLegend 
   theTheme.Invalidate(FALSE) 
   
   '-- You can set a lookup if needed. For example, your image
   '-- data went from 0 to 100 and you wanted to stretch
   '-- that data across the entire color map. The following
   '-- two lines of code will do this. Place these two lines 
   ' before theTheme.UpdateLegend above. 
   ' 
   'newLookup = LinearLookup.MakeLine(Point.Make(0,0),Point.Make(100,255)) 
   'theLegend.SetImageLookup(newLookup) 
   
   '-- It is best to start from the current image legend of an image theme,
   '-- but you can start from scratch. The code below does this.
   '-- Instead of theTheme.UpdateLegend above you would
   '-- use theTheme.SetLegend(newLegend). It is best to set a
   '-- color map of 256 colors. 
   ' 
   'anImageLookup = LinearLookup.MakeLine(Point.Make(0,0),Point.Make(255,255)) 
   'aColorMap = ColorMap.MakeRamp(256,Color.GetYellow,Color.GetBlue) 
   'newLegend = SingleBandLegend.Make(0,anImageLookup,aColorMap) 
   ' 
   '-- The above lookup is the same as the identify lookup,
   '-- or IdentityLookup.Make. It maps the values in the image
   '-- to the same value in the color map. 

   
   
3. Compile and run the script.
   
   
   A. Click the Compile button.
   
   
   B. Click the Run button.