How to Use the Channel Mixer in Photoshop CS6
The Channel Mixer in Photoshop CS6 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.
Just make a backup copy of an image before diving into the mix. Then follow these steps:
Select the composite channel in the Channels panel.
If you have an RGB image, the composite channel is the RGB channel; for CMYK images, it’s the CMYK channel.
Choose Image→Adjustments→Channel Mixer.
The Channel Mixer dialog box appears.
If desired, select a Preset from the drop-down menu (pop-up menu on the Mac).
CS6 provides an assortment of Black and White presets you can use to convert your color images to grayscale. This is a great conversion method because it preserves detail and provides very good contrast control.
For Output Channel, select 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 menu (pop-up menu on the Mac). Note that if you’re using one of the black and white presets, you have only the Gray channel available.
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 the Blue channel contains artifacts and dithering picked up by the scanner, this image has the Red and Green values raised from 0% to 25% and the Blue value lowered 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.
Tinker with the Constant option to add a Black or White channel of varying opacity.
This option adjusts the grayscale value of the selected Output channel. 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, but it may cause strange color shifts if adjusted to the extreme. It is best to leave it at 0 most of the time. But try it. It may help.
Select Monochrome to apply the same settings to all output channels, producing a color image that has only values of gray.
This is another great way to produce a grayscale image from a color image. Adjust the individual sliders to mix the values until you’re satisfied with the contrast.
You can save (and load) any of your custom settings by clicking the Preset Option button just to the left of the OK button.
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 menu (pop-up menu on the Mac). 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.