Using the Channel Mixer in Photoshop

The Channel Mixer actually does what its name implies — it mixes color channels. This feature lets you repair bad channels and produce grayscale images from color images. It also allows you to create tinted images and more intense special effects. Finally, it allows you to do the more mundane tasks of swapping or duplicating channels. Although some Photoshop elitists worldwide tout this as an advanced feature not to be mucked with by amateurs, I say, “Give it a whirl.” Intimidation is a nasty roadblock to creative fun. Just make a backup copy of an image before diving into the mix:

1. Select the composite channel in the Channels palette.
If you have an RGB image, the composite channel is the RGB channel; for CMYK images, the CMYK channel.
2. Choose Image➪Adjustments➪Channel Mixer.
The Channel Mixer dialog box appears, as shown in Figure 1-7.
3. For Output Channel, choose the channel in which to blend one or more source (existing) channels.
For example, if your Blue channel is lousy, select it from the Output Channel drop-down list.
4. Drag any source channel’s slider to the left to decrease the channel’s effect on the Output channel. Or drag to the right to increase the effect.
Because my Blue channel contains artifacts and dithering picked up by the scanner, I am raising the Red and Green values from 0% to 25% and lowering the Blue value from 100% to 50%. To retain good contrast, try to use a combo of Red, Green, and Blue values that add up to close to 100%. You can also enter a value from –200 to +200%. Using a negative value inverts the color data of the source channel.
5. Tinker with the Constant option to add a black or white channel of varying opacity.
Drag the slider to a negative value to get a black channel. Positive values give a white channel. This option brightens or darkens the overall image. I recommend leaving it at 0 most of the time. But try it. It may help.
6. Select Monochrome to apply the same settings to all output channels producing a color image that has only values of gray.
Adjust the individual sliders to mix the values until you are satisfied with the contrast. This option is one of the best ways to produce grayscale images from color images because it preserves detail and provides better contrast control.
7. Click OK to exit the Channel Mixer.
After you exit the Channel Mixer, choose Image-->Mode-->Grayscale to complete the conversion. If you select and then deselect the Monochrome option, you can modify the blend of each channel separately. By doing so, you can create color images that appear to be hand-tinted with color inks. Go for the subtle treatment or a more intensely colored look.

Swapping color channels can produce some bizarre color effects. For example, try selecting the Red channel from the Output Channel drop-down list. Set the Red source channel to 0 and then set the Green source channel to 100. Try other combinations, Green for Blue, Blue for Red, and so on. Sometimes they can be downright freakish, but occasionally you may stumble on one that’s worthy.