Channel Mixer Adjustment Layer

A good alternative to the Black And White adjustment command for converting color images to grayscale is the Channel Mixer. Once again, using the Channel Mixer adjustment layer rather than the Image --> Adjustment --> Channel Mixer command offers much more flexibility and control, because it allows you to make changes to the adjustment at any time after it is applied. The Channel Mixer is great for applying grayscale conversions to images whose colors contain noticeably different hues but similar light and dark values. It’s best to make this conversion to an RGB image. If your image is not already in RGB mode, choose Image --> Mode --> RGB Color, and then apply a Channel Mixer adjustment layer. In the Channel Mixer dialog box that appears, select the  Monochrome check box in the lower-left corner. Also make sure that the Preview check box is selected.

Move the Red, Green, and Blue sliders to modify each channel’s influence in the resulting black-and-white image. Keep in mind that the Red channel contains the most brightness; the Green channel contains the most detail; and the Blue channel contains the most noise. For a wellbalanced black-and-white image, the total for all three channels should add up to 100%. Photoshop also includes several Channel Mixer preset settings. Unless you’ve already mastered the Channel Mixer dialog box, you may want to start  out by previewing these presets first. Choose one that comes closest to the way you’d like your black-and-white image to appear, and then modify the settings as needed. If you’d like, you can also save your own custom presets.

When you are through adjusting the image, make sure that you make a flattened duplicate by choosing Image --> Duplicate and enable the Duplicate Merged Layers Only option in the dialog. Doing so retains the original image with the Channel Mixer adjustment layer. To complete the grayscale conversion on the flattened duplicate image, choose Image --> Mode --> Grayscale.