Enter Channel Mixer
As Photoshop (and the people using it) started to explore, better ways emerged to create black and white images with greater control. To create a more responsive black and white image, users began to experience with Photoshop’s Channel Mixer adjustment.
Click on Image > Adjustments > Channel Mixer, and select the Monochrome checkbox at the bottom of the window (see Figure 4). This will turn the image into a black and white image. From here, you can use the sliders in the dialog box to mix in which color is darker in the image than other colors.
Figure 4 The Channel Mixer dialog box
The problem that I usually had with this method is that one could never really tell what colors made up the image after the Monochrome checkbox was clicked. This meant that many of the sliders would be used in a guessing fashion. You clicked and dragged, and the image randomly adjusted itself. There needed to be a better way for us to produce a black and whitea way that gave the user a lot more control with the image.