A color photograph can have over 16 million different colors. A grayscale image has only 256 shades of gray. You must translate those colors to grayscale in a way that gives aesthetically pleasing results. Fortunately there is more than one way to do a conversion. If one method doesn't work on a particular photograph there are others that you can try.
All conversion methods work by taking the colors in a photograph and converting them to shades of gray. However, your choice of conversion method will affect the look of your final image. As you can see from the photograph to the right, different conversion methods can lead to very different results. There are two categories of conversion methods.
Luminosity Based conversion methods assign a shade of gray based only on the color's brightness or luminosity. This is similar to the way black and white film captures only the scene's brightness. Generally, Luminosity methods work best for photographs with high contrast.
Color Altering conversion methods alters the colors in your photograph before converting it to grayscale. By doing this, color altering methods translate color contrast into luminosity contrast. Color altering methods work great on images with high color contrast. Color Altering methods also allow you to simulate filter effects and film response.
|Luminosity Methods||Color Altering|
Destructive conversion methods covert the image by destroying the color information. Once destroyed the color information cannot be recovered. For example, the Straight Grayscale method converts the image by changing the color mode from RGB to grayscale. If you change the mode back to RGB the image is still in black and white. Even though the mode is RGB the color is not recovered. Non-destrucive methods convert the image by adding new layers to the existing image. The color information is not destroyed and can be used in later processing. Use non-destructive methods for selective conversions, stacking conversions, or if you plan on selective coloring your photo.
The question invariably comes up: "What is the best method for black and white conversion?"
There is no such thing as one best method that works for all images.Your choice of conversion method will depend on the nature of your color image and the result you want. Don't stick with one conversion method all the time. Use the method that gives the best result for your photograph. Knowing when to use Luminosity or Color Altering methods will greatly improve your chances of success.
Also, don't assume that complex methods are better than simpler methods. Don't use a complex method when a simpler method will do. Conversely, don't take shortcuts and use a simple method when a more complex method is required. With some experience you'll get a feel for which method works best for which types of image.
Having said all that, black and white conversion is an artistic rather than a mechanical process. Don't be afraid to experiment. The results may surprise you.