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color_index_to_rgba

Converts an absolute color index to its equivalent RGBA quadruplet

Available in version 6.2.0 and later.

Prototype

	function color_index_to_rgba (
		color_indexes [*] : numeric   
	)

	return_val [4]

Arguments

color_indexes

An array of absolute color indexes. An absolute color index is an integer with a value between 2^30 (1073741824) and 2^31 -1 (2147483647) that maps to a unique RGBA quadruplet. Absolute color indexes are independent of the workstation color table specified using the resource wkColorMap.

Return value

An array of unique RGBA quadruplets.

Description

Absolute color indexes are mainly encountered by an NCL user when retrieving the values of color resources such as cnFillColors using the getvalues visualization block. Absolute color indexes are created when setting colors for a plot object using any of the palette resources such as cnFillPalette, or when using a named color or an explicit RGBA value to set any color index type resource.

This function converts the absolute color index values to more humanly readable RGBA quadruplets. RGBA values and absolute color indexes can be used interchangeably to set color index type resources.

Note that currently this function does not do any checking to see that the color indexes to be converted are within the proper range. In particular, color indexes associated with a workstation color map (in the range 0 - 255) will return bogus values.

Examples

Example 1

Get and print the RGBA values associated with a color indexes of simple contour fill plot.


  T = generate_2d_array(5,5,0,120,50,(/100,100/))

  wks = gsn_open_wks("png","color_index_to_rgba_example")

  res = True
  res@cnFillPalette   =  "rainbow"
  res@cnFillOn              = True

  plot = gsn_contour(wks,T,res)
  getvalues plot
        "cnFillColors" : fcol
  end getvalues

  rgba = color_index_to_rgba(fcol)

  print("plot has " + dimsizes(fcol) + " colors")
  print("index " + fcol(:) + " represents red: " + rgba(:,0) + " green: " + rgba(:,1) + " blue: " + rgba(:,2) + " alpha: " + rgba(:,3))

Output: