Converting To Black and White Customary Method

The purpose of the Channel Mixer adjustment layer is to allow us to control the mix of each color channel to determine the resulting colors and tones in the image. Specifically, for a RGB image, it allows us to mix the various amounts of Red, Green and Blue.

Figure 1. Channel Mixer Dialog Box

The basic way to use this method is to first look at the red, green and blue channels individually on the Channels panel. Find the one that looks closest to the desired results. Reactive all channels, switch back to the Layers panel and create a Channel Mixer adjustment layer. When we first open the Channel Mixer dialog box, it defaults to Red at 100%, Green and 0% and Blue at 0% and the monochrome box is unchecked. Change the color channel in the Output Channel drop down box to the channel that looked the best on the Channels panel and then click the monochrome box. Then move the three sliders to fine tune the image. Do not change each percentage to 100%. The percentage is not how much of a channel's information is used, but it's weight in the total mix of information. Since it is usually best that the total mix of information add up to 100%, then it is usually best if the three channels add up to 100%. It is valid for a channel to have a negative percent.

Tip

Theoretically, if we use Channel Mixer to set one of the three primary colors to 100% and leave the other two at 0% and check the monochrome box, it should match the image we see on the corresponding channel in the Channels panel. I have found this not to be true. The images are very similar, but they are not exactly the same in appearance.

To make reds a darker tone, decrease the red percentage. To make greens a darker tone, decrease the green percentage. And to make blues a darker tone, decrease the blue percentage. If we increase the percentages instead, the change in tone will be reversed.

As we move the sliders, Adobe Photoshop uses each channel's percentage to determine the weight that channel's information is to be used when calculating the resulting black and white tone.

Figure 2 shows the resulting tone using the customary Channel Mixer method. Figure 2 is just one of many results that can be achieved with this method. Figure 2 was created using the Channel Mixer values in Figure 1 above.

The advantage of this method is we have control over the tones as we change the percentages. The disadvantage is the balancing act that needs to be performed to keep the total near 100%.

Figure 2. Custom Channel Mixer

Figure 3. Channel Mixer to Preserve Measured Tone

Note

The Channel Mixer method is one of the most popular customary methods. You can learn how to use Channel Mixer in the Tone Management System (TMS) to retain measured luminance on the TMS Measured Luminance page.

Customary Method - Channel Mixer