Converting to Grayscale

This guide demonstrates how to convert an RGB color value to grayscale.


To convert any color to a grayscale representation of its luminance, first one must obtain the values of its red, green, and blue (RGB) primaries in linear intensity encoding, by gamma expansion. Then, add together 30% of the red value, 59% of the green value, and 11% of the blue value. The resultant number is the desired linear luminance value; it typically needs to be gamma compressed to get back to a conventional grayscale representation.


The following example demonstrates the above algorithm…

Option Explicit

Sub ConvertLayersToGrayscale()

  ' Declare local variables
  Dim arrLayers, strLayer, lngColor
  Dim nGray, nRed, nGreen, nBlue

  ' Turn off screen redrawing (for performance)
  Call Rhino.EnableRedraw(False)

  ' Get all of the layers in the document
  arrLayers = Rhino.LayerNames

  ' Process each layer one-by-one
  For Each strLayer In arrLayers

    ' Get the layer's color
    lngColor = Rhino.LayerColor(strLayer)

    ' Get the color's red-green-blue components
    nRed = Rhino.ColorRedValue(lngColor)
    nGreen = Rhino.ColorGreenValue(lngColor)
    nBlue = Rhino.ColorBlueValue(lngColor)

    ' Calculate the grayscale based on the NTSC color gamut
    nGray = CByte(nRed * 0.30) + CByte(nGreen * 0.59) + CByte(nBlue * 0.11)

    ' Modify the layer's color
    Call Rhino.LayerColor(strlayer, RGB(nGray, nGray, nGray))


  ' Turn on screen redrawing
  Call Rhino.EnableRedraw(True)

End Sub