Choose Your Weapon

Film choice is usually a matter of how the photographer envisions a particular image. First, whether color or B&W, and then by how the particular film of choice will render the image. Among color films, for example, the choice might be for a strongly saturated film like Fuji Velvia, or the more neutral rendition of Fuji Provia or Astia. Various choices are similarly offered in Kodak's color films. Among B&W films, the choices might be based on grain, sharpness, and overall tonal response. Regardless of the original color film choice, however, the time will come when you want to see how the image looks as B&W. Prior to the advent of digital imaging, photographers would often make B&W prints of color negatives. B&W prints of Kodak color negatives with Kodak's orange mask using "normal" B&W photo paper tended to be rather flat, contrast-wise, so many used Kodak's special Panalure paper formulated specifically for making such prints. Today, with digital processing and digital printing, the process is far easier. The trick to getting a good B&W version of the color digital image, however, is a matter of how one goes about making the conversion from color to B&W. So, choose your (image editing) weapon.

Eanie, Meanie . . .

Adobe's Photoshop offers various methods for converting color images to B&W. The simplest method is to simply convert the RGB digital file to grayscale, using the command path Image->Mode->Grayscale. This approach converts the 16-bit RGB image to an 8-bit grayscale version. While this method works, the translation of color tones to shades of gray often leaves something to be desired. It is also possible to desaturate an RGB image to B&W, which works well for some images. For greater control, however, it is often best to use Photoshop's Channel Mixer, as you'll see.

straight grayscale	after curves adjustment

Grayscale Conversion - As you can see, the straight grayscale conversion results in both a somewhat muddy image, and the tones aren't quite right. Adjusting the contrast using the curves adjustment tool helps to bring back some "zing" to the image, but it is still less than optimal.

Another potential problem with a straight grayscale conversion that isn't apparent here, is that the 8-bit palette is limited to 256 shades of gray. If the background has subtle shading, such as that often resulting from use of a seamless paper background, color "banding" will result, because there aren't enough shades of gray available to accurately represent the tones in the original. As such, it is often better to leave the image as a 16-bit RGB file, and use some other method for the conversion to monochrome, even though that will result in a larger file size. Remember, file size is one of the factors you want to think about when working with images destined for display on the Web.

RGB desaturation	the initial image histogram	after adjusting Levels

RGB Desaturation - Using the Image->Adjust->Desaturate tool also works to convert the RGB image to monochrome. As shown above, however, the plain desaturation isn't quite right, either. A look at the histogram shows why - the converted image lacks true blacks, and the white point is too far to the right of the image data. Adjusting the Levels brings the image more in line with what one would expect, as shown by the final desaturated version on the right.

Red Channel	Green Channel	Blue Channel

Channel Mixer - The Channel Mixer (Image->Adjust->Channel Mixer) enables each of the RGB channels to be adjusted individually. Just click on the "Monochrome" box at the lower left, and the channel mixer initially uses the red channel set to 100%. Reduce the red channel to a value less than 100%, and then mix in the green and blue channels as desired to achieve the tonal balance that is most pleasing to you. However, be sure to keep the total of the three values equal to 100%, or the image will start to wash out, tone-wise. How you choose to mix the channels will depend largely on the color mix in the original image. You can also use the "Constant" value to add a constant value for each of the channels. If so, then simply reduce the individual channels so that the overall total still adds up to 100%. For many average scenes, either landscapes or portraits, for example, I find that a mix of 65% red, 25% green, and 10% blue works well.

For this image of the red rose against a dark gray background, I chose a mix of 50% red, 28% green, and 22% blue, knowing that I'd want to make a minor adjustment in Levels after making the conversion. Comparing this screen capture with the one above showing 100% red, however, you can get a good idea of the effect of mixing in the other channels. While the 100% red channel makes the rose look almost white, adding in the green and blue channels brings the values to a more natural level, making the rose appear more like it would with a conventional B&W film shot.

You may find a certain mix that works well for you on a group of images of a particular type or color film. The Channel Mixer allows you to save the settings, and apply them to other images in your work flow. Simply click on the "Save" button, and it will prompt you for a file name. If you save several different settings, you may find it handy to include the values in the file names.

Finally, Final - So, after exploring some of the Photoshop options for color-to-B&W conversions, we end up with this version of the original, settling on the Channel Mixer version with a touch of Levels adjustment after the conversion to boost the contrast a bit. OK, "we" may be a stretch here, as I did all of the choosing, but you get the drift.

Although you may end up using one of the choices for most of your B&W conversions, some images benefit from trying a couple of different methods to see which will work best for that particular image. Again, it's a matter of the colors in the original, the tonal range and contrast of the original, and your own personal tastes. No single approach works for every image or every photographer.