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Black and White, the digital way
This article is an extended version of one Keith wrote for Canon Europe (issue 11). It is aimed to show the basic principles involved in digital black and white photography. The quality of conversions is discussed later, since if you are going to be producing the best black and white prints, the conversion technique can make quite a difference. There is also more information on conversion and printing in the Digital Black and White section.
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High quality Black and White
Black and white goes back to the very origins of photography. Early plates and films had limited sensitivity to longer (red) wavelengths of light and produce a certain interpretation of the subject. Later films had a much more even response to colours (panchromatic) that led to a different ‘look’. The differing chemistry and manufacturing processes adopted by various manufacturers resulted in different films producing subtly different renditions of the same scene.
Hood Canal, Washington – from a Canon EOS 1Ds raw (colour) image
It was soon discovered that using coloured filters in front of the lens also altered the image. For example, a red filter cuts out some of the blue light from the sky while still letting through the red component of the white light reflected from clouds. This results in darker skies, which emphasise the clouds. More complex mixtures of colours, such as flowering plants and skin tones, would all look slightly different on different films and with different filters.
Going digital
OK, so I have my digital camera and want a black and white picture of a landscape, with dark skies and fluffy white clouds, what do I need to do?
Some cameras do indeed have a black and white setting that might be worth a try, but I’m looking a getting the very best out of my camera and want to use ‘raw’ images, just the same as I would with colour. The black and white setting gives you 8 bit black and white JPEG images. If you shoot raw and JPEG at the same time you’ll find that the raw files are still in colour.
I’m going to be looking at converting the raw files to colour and then to black and white. The examples all used Photoshop CS for raw conversion and subsequent image processing. You could use other raw converters and photo editors just as well.
In my own work I often apply some fairly hefty curves and adjustments to my black and white images. Posterisation can be a real problem if you are working with 8-bit images (such as from JPEGs). One way to reduce the risk is to work in 16-bit where you have more data to play with
Sky and clouds -- filters
Back to the sky and clouds…
I compose and take the picture just as if I had black and white film in my camera.
Well not quite, with film I might select a filter, maybe a light orange filter – red often looks too much like moonlight.
With digital I can still apply the equivalent of a coloured filter for black and white, but I’m going to do it later with Photoshop. I also have the advantage of changing my mind if I decide, for example, that a yellow filter would have been better. It is true that the process is not quite equivalent, but certainly very similar.
The two black and white images of Tower Bridge below show some of the subtle changes that you get with different processing
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The RGB colour original |
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Simple conversion RGB to grayscale |
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Layer based technique. (See later for layer settings) |
Basic conversion techniques
For all of the conversion techniques I’m going to describe, I’ll assume that you have a well-exposed raw file with very little clipping of highlights. By all means experiment with any pictures you want, but starting with good colour originals allows you to see the effects of different conversion processes more easily.
Digital cameras are thought of as recording scenes in pixels of red, green, and blue. Actually each pixel is sensitive to a range of colours and has a little coloured filter in front, so it is more accurate to think of each one contributing to a grayscale image (channel) representing values of mostly red, mostly green and mostly blue. This gives one of the simplest conversion techniques, just pick one of the channels – it’s already in black and white. If you want to use the red channel, delete the green and blue channels and change the image mode to ‘Grayscale’
Very simple, but you are throwing away a lot of your picture information, and for the best quality, that’s not really what we want.
There are several other simple techniques available in Photoshop:
- Change the mode to grayscale: Image>Mode>Grayscale
- Desaturate the image: Image>Adjustments>Desaturate
- Change the mode to Lab: Image>Mode>Lab Color --then delete the ‘a’ and ‘b’ channels, and change the resulting Alpha channel to Grayscale.
The Lab, Grayscale, Red channel, Green channel and Blue channel processes are compared in this Wyoming landscape.
If you move your mouse pointer over the picture, the coloured original will be revealed.
Layer based effects
What if you mix the 3 different channels as grayscale images?
Easy to do, with a ‘Channel Mixer’ adjustment layer
Note the ticked monochrome box.
The percentages are the proportions of the different channels that are being mixed. They do not have to add up to 100% but it is a useful starting point.
This method allows you to fine tune the conversion to emphasise different aspects of the coloured original. Remember that something like ‘blue’ does not really equate with any particular shade of gray, it is how the tone relates to others that gives the effect.
Although very powerful, you are mixing just three channels and there are times you may want finer control.
A very simple technique (used in the second Tower Bridge picture) involves just two Hue and Saturation (H/S) adjustment layers.
- Create a H/S Adjustment layer with no adjustment. Change the layer blend mode to Color
- Create another H/S Adjustment layer with Saturation at minus 100.
- Return to first H/S layer and tune the black and white effect using the Saturation and Hue sliders
The Tower Bridge picture had Hue -36 and Saturation +42.
Even more detailed control is possible by using different edit selections in the adjustment dialog. This allows you to select which colours are altered by differing amounts.
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This picture of a cottonwood tree was taken in Wyoming.
If you move your mouse over the image you will see the results with 2 H/S layers with settings of Hue –43 and Saturation +25 If you click on the picture and hold the mouse button down you will see the ‘Infra-red film look’ that uses settings of Hue +19 and Sat +75 but has the blending modes reversed (first layer ‘normal’, second ‘color’) |
I found the second 'Infra Red' technique accidentally, when experimenting with blending modes. Remember that there are no ‘right’ ways of getting your black and white image and it is well worth trying different options. You could for example try a H/S layer with a channel mixer layer (monochrome) above it.
I’ve only listed some of the simplest methods here. You can combine them, mask them and generally spend a lot of time ‘getting it right’ if you want. There are a number of third party plugins available for Photoshop, some of which even aim to mimic the responses of particular film stock. I've got a collection of most of the methods I've found on the B/W conversion page.
You can also try conversions directly in Adobe Camera Raw, by setting the saturation to –100 and altering the other settings under the ‘adjust’ tab.
Conversions and quality
Seeing results on the web, there may not look too much difference between the techniques, but when you are looking to make high quality prints, there are some other considerations in deciding which to try.
Work in 16-bit mode if possible. The image of Hood Canal at the start of this article would have been seriously posterised if I’d worked in 8-bit.
Any method that pushes saturation of an image too far is likely to show artefacts. This is particularly true at high ISO speeds or with compressed (JPEG) original images. The Tower Bridge layers example and first cottonwood conversion, both use more saturation than I would normally use for prints. This was mainly so as to show the effects more clearly in this web article.
Image noise may be more noticeable in some channels. The blue channel often shows this up, particularly in deep blue skies.
With my landscape prints I often use the Lab method since it seems to give files that are easy to work with and take large adjustments well. As with most of these things you should experiment and see what works best for your images.
Welcome to digital black and white!
There is more info in the Digital Black and White section of the site
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