By using the Desaturate command, you can convert all of the colors on the active layer to corresponding shades of gray. This differs from converting the image to grayscale in two respects. First, it only operates on the active layer and second, the colors on the layer are still RGB values with three components. This means that you can paint on the layer, or individual parts of it, using color at a later time.

	Note
	This command only works on layers of RGB images. If the image is in Grayscale or Indexed mode, the menu entry is insensitive and grayed out.

5.9.2. Options

Figure 13.155. The “Desaturate” option dialog

Three options are available:

Choose shade of gray based on

Lightness

The graylevel will be calculated as

Lightness = ½ × (max(R,G,B) + min(R,G,B))

Luminosity

The graylevel will be calculated as

Luminosity = 0.21 × R + 0.71 × G + 0.07 × B

Average

The graylevel will be calculated as

Average Brightness = (R + G + B) ÷ 3

Figure 13.156. Comparing the three options

Original image

“Lightness” applied

“Luminosity” applied.

“Average” applied.