A Method for Black & White Conversion

September 18, 2013  •  Leave a Comment

There are many different methods one can use for black and white photo conversions, and generally speaking all conversion methods can be categorized in a good / better / best structure. This article discusses one technique that I consider to be better than most. I would like to tell you this technique is the best method but that would be a matter of opinion. Just as people have preferences for color saturation and contrast, people also have their preferences for what appeals to them in black and white images. I mainly use this method because it gives me a great deal of control of how the tones of the primary and secondary colors are blended during the conversion process.

This method can be achieved in any software that offers HSL (hue, saturation, lightness) adjustments. The basis of this method simply adjusts the luminosity (or brightness) of the colors to achieve the black and white balance and contrast that suits your preference. To say that another way, when you decrease or increase the luminosity of a specific color within a black and white image, the corresponding tones become darker or lighter.

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Today I use Lightroom for approximately 75% of my black and white conversion work. To the left is a screenshot of Lightroom's adjustment panel for B&W images. The appearance of the HSL panel may vary between image editing programs but typically they all do the same job. The adjustment sliders you see to the left represent the luminosity of the primary and secondary colors that may be present in a photograph. 

Look at the left and right ends of each slider and you will notice they are darker on the left and brighter on the right. One simply moves the slider to the left or right to adjust the luminosity of that color.















The sunflower photographs below illustrate how we might adjust the luminosity of a color to achieve different effects. Image A is the original color photo. Image B shows the photo converted to black and white by only desaturating the image (simply removed the color). Note the HSL adjustments for image B; they are still sitting in the middle which represents the "natural tone" of each color when simply desaturating the photograph. One of my personal preferences when converting to black and white is to use a dark sky. Image C shows how that is done by reducing the luminosity of the blue channel.

A) Original photo B) All color desaturated, but with no tonal adjustments to any color C) Tones for blues and aqua reduced to create a much darker sky
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Beware of Posterization

One of the problems with many black and white conversion methods is posterization occurring during the conversion process. Look at the basic HSL adjustment panel below and notice how the colors flow within the adjustment sliders: Orange occurs between Red and Yellow, Blue occurs between Aqua and Purple, and so on. Posterization can occur if you create a wide divide in the tones that lie very close to or in between the primary and secondary colors. The posterization you see in the image to the left - the banding that occurs when tones are stretched too far - is an exaggerated example of the nasty effect. 

Finally we'll look at a landscape image that required multiple HSL tone adjustments to achieve my vision. The HSL adjustment panel below and right represents the landscape photo you see below. Let’s start with the boldest characteristic of this image by looking at the Blue slider. You’ll see the slider is set to -80. This translates to reducing the luminosity of all blues by 80%, or making the blues 80% darker than how the camera captured the color. And the effect is seen in the dark areas of the sky that I love so much! Those dark areas could be pushed all the way to black by moving the blue slider all the way to the left (to -100). The same principle applies to all primary and secondary colors available in your software’s HSL adjustment feature. Let’s also look at the Red and Yellow sliders. Notice they are pushed all the way to the right at +100 and into the light end of the slider.

The Reds: Look at the roof of the barn and the roof of the smaller building to the far left. Both buildings have rusty metal roofs which contain a high amount of red. I have pushed the reds to +100 to make the roofs’ tones flow with their surroundings to suit my preference. Those roofs could easily be pushed to black by setting the slider to -100. The Yellows: The yellows in this image appear in four primary areas – the fence, the dirt and grass in the middleground, the wood siding of the barn, and the highlights in all the trees. For the most part I set the yellows to +100 to bring out the highlights in the trees and barn siding but again, that was only my preference. It is quite possible that you would have interpreted those tones differently to suit your own taste.

You can see how I handled any concern of posterization in this image by adjusting the Aqua and Purple sliders. I have reduced the luminosity of both colors along with the blues to help create a smooth gradient, or transition, of tones between the three colors. 

Why didn’t I adjust the Orange and Magenta sliders? Well, I did. I make a habit of moving every slider in both directions to see how it affects the image globally. Moving each slider back and forth several times and observing the changes will help you see where each color exists throughout the image and how the shifts in tones affect adjacent tones. To my eye the orange and magenta adjustments in this image were of no consequence so I left the sliders at zero.

Why go through all the trouble?: Have you ever tried to see in black and white? I know that sounds crazy and admittedly it can be difficult to think of having black and white eye vision. But the idea is to look beyond the color saturation and begin comparing tones. When you begin to think in this manner you quickly realize how similar the tones are in things that are all around us. Let me provide you a good example with the comparison shown here. The black and white image is a simple desaturation of the color photo - the color was simply removed and no tonal adjustments were made. In the color photo we easily recognize the difference between the flower and the brick but when we strip away the saturation, you can then see just how close the tones are between the flower and the brick. 

The conversion method I’ve discussed here is the solution to problems like this and allows you a tremendous amount of latitude for interpreting a scene many different ways. 



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