Choosing a graphic program
Numerous programs such as Adobe’s Photoshop, Elements and Lightroom, Apple’s Aperture and iPhoto, PictureCode’s Photo Ninja, Corel’s AfterShot Pro or PaintShop Pro, ACDsee and Gimp on Linux to name a few, have the ability to alter image characteristics and appearance. You can freely choose which one to use because they offer similar graphic tools and filters. I have used Adobe Photoshop CS6 and I will refer to its functions in this article, nevertheless you should observe that additional programs have a similar functionality even if the name of the functions may differ. If you are an Adobe Lightroom user you will surely find interesting a previous article from Josh Larkin.
You can find more articles and others in the software section of Nikonians.
Basic function - Desaturation
The easiest and fastest way to make a B&W photo is to desaturate the image with the Desaturate function or with turning the Saturation level to zero (Image – Adjustment – Hue\Saturation). This method is quick but you will achieve the same look as with the in-camera B&W filter and the image will have the exactly look I would like to avoid. Desaturating an image means to throw the color information away leaving only the brightness information and this is why the image looks so flat.
A really great function, from which you can learn the behavior of colors, is the Channel mixer (Image – Adjustment - Channel mixer). One has to mark the checkbox saying “Monochrome” and then adjust and play around with the moving scrollbars. Unlike the previous destructive method which threw away all color information, Channel mixer works with the primary colors as well, so when you move e.g. the Red scrollbar by + 20%, all reds in the image will be emphasized by 20%. This function follows a rule that the overall tonal range of the image is 100%; this means when you mix the red, green and blue in a ratio of 100% the image should not be over- or underexposed. But you are not limited by the 100% value. You can freely choose a higher or a lower value with all of the three colors. I call this function great because it gives the user a basic understanding of how a color filter works. By filtering a specific amount of light of a specific color, a black and white image immediately changes its visual characteristics.
A dedicated Black & white filter
A tool specially developed for B&W photography conversion is to be found in Image - Adjustments - Black & white filter. It has a very similar, but more advanced, functionality with more options available as the previous Channel mixer. Besides the reds, greens and blues you can control the yellows, cyans and magentas by which you get more control over the color nuances. You may find the predefined filter settings immensely helpful as well.
A B&W image with a yellow-green filter accentuates the textile textures and softens the skin tone.
The picture of three primary color circles - RGB
The picture of RGB circles is a good example how to explain the use of a color filter. I will now use the Channel mixer and filter only one color; let's take the red color as an example. I will apply an absolute red filter. That means the red color gets a 100% value and 0% green and blue color. With a full red filter only the reds of an image are visible and only their luminance is taken into account, therefore the additional parts, circles in this case, disappear. If I would filter only the greens (100% green, 0% both red and blue) then what is green in the picture would appear and the rest would not be visible. As you see, it is possible to make endless combinations of filtering colors, playing with percentage values and different variations. A general rule of thumb says that a color filter will lighten colors similar to its own and darken those opposite. To lighten an object, one has to choose a filter of the same color as the object.
“Why would you do that?” you may ask. Remember, your image is not originally black and white until it is actually processed by the graphic program. A colored filter will alter colors as seen by the camera and change the representation of captured colors. A wise usage of a filter will grant your image a pleasant look and a truer rendition of the grey tones.