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rgba_to_color_index

Converts RGBA quadruplets to their encoded integer equivalent absolute color indexes

Available in version 6.2.0 and later.

Prototype

	function rgba_to_color_index (
		rgba [*][4] : float   
	)

	return_val [*]

Arguments

rgba

A 2D array of float type rgba values or a single 1D rgba value. The rightmost dimension must have 4 elements, and the valid values for each element must be in the range [0.0 - 1.0].

Return value

A single dimensioned array of absolute integer color indexes.

Description

This function converts RGBA quadruplets into absolute color index values. RGBA values and absolute color indexes can be used interchangeably to set color index type resources. Absolute color indexes specify a particular color independent of any workstation color map. Since a single integer color index represents 4 floating point values, it may be more convenient or efficient to work with absolute color indexes in some situations.

Examples

Example 1

Get and print the absolute color indexes associated with the rgba values in an NCL system colormap.



  cmap_name = "seaice_2"
  cmap = read_colormap_file(cmap_name)
  cix = rgba_to_color_index(cmap)

  print("The " + cmap_name + " colormap has " + dimsizes(cix) + " colors")
  print("rgba value (" + cmap(:,0) + "," + cmap(:,1) + "," + cmap(:,2) + "," + cmap(:,3) +") is represented by color index " + cix(:))

Output: