# Converting to Grayscale

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

## Overview

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.

## Example

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))

Next

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

End Sub