Converting an image from color to black and white (or grayscale, if you're a stickler for accuracy) is a tricky proposition, because there are no objective rules about which shade of gray corresponds to which color. In a black-and-white landscape photo, you can just as easily represent a clear blue sky as dark black or very light white, and both effects can look fine depending on the image.
There are almost as many techniques for performing black-and-white conversion as there are for performing red-eye reduction. In Photoshop, the most basic technique is simply to choose Mode > Grayscale. A Grayscale mode change, however, gives you no control of how your colors will be converted to gray shades. Although the results can be attractive, the lack of control can be frustrating for a user who has a particular result in mind.
In CS3, when you choose Grayscale mode, you get the dialog box shown in Figure 3.13. As it explains, there's a new Black & White option available in the Image > Adjustments submenu.
Figure 3.13 When you choose Mode > Grayscale in CS3, you'll see this dialog box.
Black and White
The Black and White dialog box is really a souped-up Channel Mixer. The options here let you specify exactly how you want particular color ranges in your image to be converted to grayscale (Figure 3.14).
Figure 3.14 The new Black and White dialog box gives you a tremendous range of control for performing grayscale conversions.
The sliders are very easy to use. If you move the Reds slider to the right, for example, the red tones in your image will be represented by lighter shades; move the slider to the left, and the reds will darken. The same is true for all the other sliders. You can also adjust the tone of a particular color by clicking that color in your image and dragging left and right. Black and White will automatically determine the color of the pixel you clicked and adjust it just as if you were dragging the relevant slider.
The Black and White dialog box functions very differently from the Channel Mixer. In the Channel Mixer, if you increase the percentage of the blue channel, the blue values of every pixel in your image increase, so colors that have blue components brighten. The Black and White dialog box is much smarter than that. If you increase the Blues setting, only those tones in your image that are truly blue increase.
Consequently, unlike with the Channel Mixer, you don't have to worry about the total percentage values of your image. If the totals add up to more than 100 percent, you won't see a change in overall exposure in your image.
Also note that the sliders aren't interrelated. If you want to increase blue, you don't need to decrease yellow too. The control is smart enough to know which pixels need to be affected by a particular edit.
The Auto button performs an automatic conversion and is well worth experimenting with. The Auto algorithm does a very good job of mapping different colors to different tones to produce a nice contrasty image.
The Black and White dialog box also includes tinting controls, so you can perform black-and-white conversion and color toning in one step.
Check the Tint check box to activate the tint controls; then select the hue that you want to tint with and adjust the Saturation slider to specify the strength of the tint.
The Black and White dialog box is equipped with several Preset configurations (Figure 3.15). In addition, you can save your own presets by using the Save and Load pop-up menu located to the immediate right of the Preset menu.
Figure 3.15 The Black and White dialog box provides a full collection of presets for achieving different looks.
The Black and White dialog box has not replaced the CS2 Channel Mixer; it's still available in the Image > Adjustments submenu, and for the most part, it's still the same (Figure 3.16).
Figure 3.16 The Channel Mixer has gained a Preset menu and a Save and Load pop-up menu.
It's been updated with the new Preset menu and a Save and Load pop-up menu, and it now offers a handy Total readout below the RGB sliders. To determine whether your channel mix will leave your image over-exposed or underexposed, you need to know the total percentage change of your channel adjustments. This readout saves you the trouble of adding up the numbers yourself.
In the face of the Black and White dialog box, why is there still a Channel Mixer? There are times when you want to mix channels to create color effects rather than black-and-white effects. By clearing the Monochrome check box at the bottom of the Channel Mixer dialog box, you can mix channels to alter the color in your image.