Oaktree Imaging

Digital Black & White

Part One: Basic Methods

by Daniel Neeley

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This first part of the series will cover the simplest of techniques for B&W conversion. Each of these techniques offer little to no customization or creative control.

Next to each method is an example conversion based off the original color granger image you see to the right. The color granger is a mathematically derived image designed to represent the full spectrum of colors possible in a particular color space (in this case it was created in sRGB for the purpose of web viewing). I am using this instead of a photo because this provides a full range of colors and luminosity values to give you a better idea of the effects of each method.

Desaturate

The desaturate method is the simplest way to convert to B&W. Simply go to Image » Adjustments » Desaturate (or Command+Shift+U).

Hue/Saturation produces the same results but benefits from the ability to use it as an Adjustment Layer that dœs not permanently affect the original image. To bring up the HS adjustment layer go to Layer » New Adjustment Layer » Hue/Saturation… or click on the Create New Adjustment Layer button at the bottom of the Layers Palette.

With the Hue/Saturation dialog box up, select the Saturation slider and drag it all the way to the left.

The problem with desaturation is that is simply strips out the saturation value of an image without any consideration as to how bright a color might appear to the human eye. This can sometimes produce unnatural results with some kinds of images (such as an image containing bright lights). In some cases it can even reduce sharpness and more often than the others, introduces posterizaton. Naturally, the severity of these issues depends upon the image. The biggest problem with using this method is the lack of creative control you have in the tonal values of your B&W image.

Grayscale

Like desaturation, Grayscale is limited in terms of creativity and control. On the upside however, you do get better contrast and more accurate luminosity. It also reduces the image from three channels (RGB) to one effectively cutting the file size to 1/3^rd of what it was. On the downside of that you have to convert it back to RGB for some printers.

Grayscaling occurs via a sophisticated standard based on how the eye interprets color. Essentially it uses 30% of the Red channel, 60% of the Green channel, and 10% of the Blue channel to achieve it’s results. It isn’t the same as the Channel Mixer though so the results won't always match exactly with those same Channel Mixer values.

There is only one way to grayscale:
Image » Mode » Grayscale

Lightness Channel

Lab Mode’s Lightness Channel is, in my opinion, the best of the basic B&W conversion methods. It preserves the correct luminosity of the image by discarding the color channels in Lab and it tends to provide the best contrast without tweaking.

Gradient Map

The Gradient Map applies a gradient mapped to the luminosity levels of an image. As seen in the example conversion, no differentiation is made to colors.

Color Blend

Here we’ll use Color blending with a solid black layer. As can be seen in the example, this essentially produces the same effect as a gradient map.

Your Friend Contrast

You may noticed after using these techniques that your images seem a bit dull. This is simply part of the conversion process. When you remove the color, you remove the contrast (between colors) that the color was creating. In order to correct this, additional contrast may be needed to bring the image back to life.

This is done best using Curves (Layer » New Adjustment Layer » Curves…) as it gives you the greatest level of control. If you aren’t sure how to use curves, I recommend you read Curves Primer at Luminous Landscape.