ABSTRACT
Black and white from color When you change a color image from RGB to Grayscale mode in Photoshop, the tonal values of the three RGB channels are averaged out, usually producing a smooth continuous tone grayscale. The formula for this conversion roughly consists of blending 60% of the green channel with 30% of the red and 10% of the blue. The rigidity of this color to mono conversion formula limits the scope for obtaining the best grayscale conversion from a scanned color original. This is what a panchromatic black and white film does, or should be doing rather, because there are slight variations in the evenness of emulsion sensitivity to the visual and non-visual color spectrum. And it is these variations in spectral sensitivity that give black and white films their own unique character. But the point I would like to make here is that just like a grayscale conversion in Photoshop, a black and white film interprets color using a standard formula. You may also be familiar with the concept of attaching strong colored filters over the lens to bring out improved tonal contrast in a monochrome image. The same principles can apply to converting from color to black and white in Photoshop, and of course this allows you the freedom to make this decision after the photograph has been shot. Using the Channel Mixer, you can create a custom RGB to grayscale conversion. This gives you the latitude in Photoshop of being able to make creative decisions at the editing stage that will allow you to simulate the effect of shooting using black and white film with a color filter placed over the lens at the time of shooting. I have included an alternative technique on page 328 for producing a monochrome image from a color original, which simultaneously uses the Hue/Saturation image adjustment to modify the hue color of the underlying image and at the same time a second Hue/Saturation layer neutralizes the color to create a neutral, monochrome image.
