This page is from April's tips of the Vancouver Photo Workshops. I've copied it in case you missed the tips page.
This page contains tips, tricks and useful advise for photographers of all levels. This can be a technical hint, business advise or conceptual in nature. This month, our instructor Marc Koegel submitted the following:
Digitally Filtering Color Images for Better Black and White Conversions:
One of the most frequent questions I get asked by my students concerns the area of color to black & white conversions in Adobe Photoshop. Since most digital cameras will only allow you to photograph in color, those of us (like myself) drawn to monochrome images have to come up with an efficient way to convert color originals. The goal of this excercise is to achieve the best possible grayscale rendition of our original color photographs.
Let's start with a suitable color image that we would like to convert to greyscale...
Many (I mean a lot) of people seem to use Photoshop's Image > Mode > Grayscale method to convert RGB images into greyscale. Using this method sacrifices both control and quality, as we are eliminating (deleting) much of the original image's data.
The above image converted using Photoshop's Image > Mode > Greyscale method. The result is far from perfect and we had no means of fine-tuning the conversion process.
There are several methods we can use to improve the quality of our Color to greyscale conversions. A simple, yet effective method is using the Channel Mixer in Adobe Photoshop. This method is very quick and easy, yet allows us to have much more control over the conversion process.
Using the same color image as a starting point, this conversion method used Image > Adjust > Channel Mixer which allows us to fine-tune the amounts of Red, Green and Blue that convert to Greyscale.
Clearly, we can see how much more control over the conversion process we had using the Channel Mixer method. Even if you like the result of the first method better, you cannot argue the fact that having greater control almost always leads to a better end result. In this example, I adjusted the image to look more dramatic and contrasty, and increased the amount of seperation of the cottage to the background mountains.
When using the Channel Mixer, make sure to select the monochrome option before you fine-tune your adjustments. Some people will tell you to make your adjustments so that the sum of the individual adjustments equals 100, but from my experience this does not always hold true. My adjustment for the above image read: + 140 Red, -40 Green and + 30 Blue.
If you would like to fine-tune your conversions even more, try selecting parts of an image and converting with different color amounts using the Channel Mixer. Try to experiment!
Another great method for color to greyscale conversion can be found on Greg Gorman's site, under the "learn' navigational heading. Allthough a bit more complicated, it is very well explained and the method works great. Information is provided as a downloadable pdf document.