Using the Channel Mixer Adjustment
The Channel Mixer adjustment is the tool of choice for adjusting individual color channels, or for making an image conversion to black and white. The Channel Mixer adjustment modifies the selected output channel by blending it with a mix of the existing image color channels. Since color channels record information using shades of gray, you're essentially adding or subtracting grayscale information, not color information like the Selective Color adjustment. That's what makes the Channel Mixer adjustment ideal for converting images into grayscale.
Use the Channel Mixer Adjustment
Open an image.
Click the Image menu, point to Adjustments , and then click Channel Mixer .
Click the Output Channel list arrow, and then select from the available output channels.
Drag the Source Channel sliders right or left to increase or decrease the colors in the active image.
Drag the Constant slider left or right to adjust the grayscale output of the active image.Dragging to the left adds more black to the image; dragging to the right adds more white.
Select the Monochrome check box to convert the colors of the image into shades of gray.
Select the Preview check box to view changes to the active image.
Click OK .