Applying the Color Blending Mode
You can also convert a color image to grayscale using the Color blending mode. This method of conversion tends to produce the finest results. Details remain crisp and dark areas don’t lose definition like they do when an image is converted using color modes.The following directions show how to apply the color blending mode using a fill layer. You can also just fill a regular layer with black using the Paint Bucket tool, and then change the blending.Here’s how:Open the image you want to convert to grayscale.
Select the layer containing the image in the Layers palette.
Click the Create New Fill or Adjustment Layer button at the bottom of the Layers palette and choose Solid from the menu.
Select black in the Color Picker.
Click OK to close the Color Picker and create the fill layer.The fill layer appears in the Layers palette, as shown in Figure 34-4. Your image in the image window disappears behind the solid black fill layer.

Figure 34-4: The solid black fill layer appears in the Layers palette.
Use the Blending Mode drop-down list at the top of the Layers palette to choose Color.The image colors blend with the black fill layer to create a grayscale image, as shown in Figure 34-5.

Figure 34-5: An image converted to grayscale using the Color blending mode retains its fine detail.