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Black and White Photography (part 2)
At the end of the previous section we stated that, despite nearly all digital cameras having a black and white mode, it is always better to shoot in colour and convert to monochrome later. By doing this, you have complete control over the conversion process, and you'll retain the option to keep the colour version if it turns out to look better than in black and white.
Note however that if your camera has the option to store images in both RAW and JPEG simultaneously, then selecting black and white mode which allow you to review the black and white version, while the RAW file will always contain the original colour information straight from the image sensor. It is this RAW file that you should use as the basis for any photo editing and the conversion to black and white (even if your camera created the B&W JPEG file for you).
Conversion To Black and White
The are many options available to you to convert your colour image into monochrome - the ones available depending on the software you use. These include:
- Greyscale
- Desaturate the image
- The Channel Mixer
- Use LAB mode
- Luminosity Blending
- Calculations (e.g. Red-Red-Multiply)
- The Black and White Dialog ('Enhance' menu in Elements)
So let's take a look at these.
Convert to Greyscale
(Photoshop: Image > Mode > Grayscale)
This is the simplest way to create a black and white image from a colour phorograph (and probably produces the closest image to what the camera would have come up with if using the black and white mode). Because it is so simple, it is often dismissed as not worth bothering with. However I would say that because it is so simple, surely you should give it a quick go - you can always hit undo if the image comes out looking very flat.
Note that this option will automatically reduce the image down to a single channel image. However many image editing filters and effects require a 3 channel image to work, so you may then need to convert the image back to RGB mode (although it will remain grey as the colours already been thrown away).
Desaturate
(Photoshop: Image > Adjustments > Desaturate)
Another simple method that actually produced quite a different black and white image from the 'Convert to Grayscale' option. Sometimes it can look better, but often it can leave colours looking a little flat. It does have the advantage that it leaves the image as an RGB image, and therefore you can apply all the usual effects and filters.
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Original image
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Convert to Greyscale
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Desaturate
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The Channel Mixer
(Photoshop: Image > Adjustments > Channel Mixer)
Since the image sensor is your camera is a colour device, creation of a black and white image must be derived from this. And since there are three primary colours that come from the sensor, and a black and white image contains just one channel of information, there must be some element of weighting involved (i.e. how much of the red, the green and the blue should be used to make up the shade of grey).
Ever since the dawn of photography when black and white was the only option, photographers used coloured filters in front of the lens to either increase or reduce the brightness of a particular colour (a red filter on a blue cloudy sky would exagerate the contrast in this area in the black and white image).
This may be initially confusing. Why would a red filter do this to a sky? All that is happening is that the red filter is allowing red light through and blocking others. Colours that get blocked appear darker, blue is getting almost entirely blocked being at almost the total opposite of the spectrum to red and so appears very dark.
If you want more control over the conversion process, the channel mixer acts a little like these filters. It allows you to control the weighting of the three primary colours - which one(s) you want to give more bias to in the resulting image.
You will generally see at least three sliders labelled red, green and blue. There will probably be a check box labelled monochrome which needs to be selected if you want the output to be a greyscale image. The values of the three primary colours should add up to 100% if you want the resulting image to have the same average brightness as the original.
Setting red to 100% and green and blue to 0% will show a bright area corresponding to the areas of red in the image. If you want to mimic the luminosity received by the human eye, you should set the values to 30% (red), 59% (green) and 11% (blue)
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Original colour image
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Channel Mixer set to 100% red
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Channel Mixer set to 100% green
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Channel Mixer set to 100% blue
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From the images above, you can probably see why black and white film photographers still like to keep a red filter in their camera bag.
Hue-Saturation Adjustment Layer
This is a very flexible format for black and white image conversion is it keeps the original colour image (on the background layer) in tact while allowing you to work with the black and white image.
Although the effect can be similar to the Desaturate option above, using a Hue-Saturation Adjustment Layer offers you a similar level of control to the channel mixer. In fact, if you use two Hue-Saturation adjustment layers, you will have even more control. Try this ...
1. Create two hue-saturation adjustment layers.
2. On the uppermost one, set the blending mode to 'color' and the saturation to -100.
3. You can now adjust the hue slider on the lower one to select the colour filter you want to emulate, and the saturation slider in this layer to control the amount of effect the filter has.
This is worth having a play around with and see what effects you can get.
Use LAB mode
(Photoshop: Image > Mode > LAB Color)
LAB mode is just one of many colour spaces that Photoshop (and other packages) are able to use to represent the range of colours possible in an image. Like RGB, it is a 3-channel colour mode. However, whereas RGB mode uses the amount of each of three primary colours, LAB uses a lightness channel and two colour channels. Therefore if you convert your image to LAB mode, and then click on the Lightness channel in the Channels Palette, you will see the black and white image. To delete the 2 colour channels now, simply change the mode to greyscale and the colour information is removed from the image.
Although LAB colour is based on the human perception of colour, black and white images created in this way often appear too light to too dark. There is a technique called luminosity blending which can correct for this.
Luminosity Blending
This is one of the more complex methods of converting a colour image to black and white. It involves putting the photograph onto a layer above a plain white layer, and then changing the blend mode from 'Normal' to 'Luminosity' (called Luminance in Paint Shop Pro).
Here's a step by step approach for Photoshop users:
1. Promote the background layer with your photo on to a normal layer by renaming it or double-clicking on the word 'Background' in the layers palette.
2. Insert a pure white layer beneath the picture layer (any colour other than white, grey or black will add a tint to the picture)
3. Set the blend mode of the picture layer to Luminosity.
Too Light or Too Dark?
Some of the methods above may end up creating an image that is a little too light or too dark (the LAB mode method is particularly prone to this). If you want to create a dramatic black and white image, then try using 'multiply' or 'screen' blending. Follow these steps (written for Photoshop but probably easy to do in most other packages).
1. If you used the Luminosity Blending method above, flatten the image so that it exists on a single layer. Otherwise skip straight to the next step.
2. Duplicate the layer you now have so you have two identical layers
3. If the image is too light, set the blending mode on the top layer to multiply. If this now makes the image too dark, use the opacity slider for the layer until you get the desired brightness.
4. If the image is too dark, set the blending mode on the top layer to screen. If this now makes the image too light, use the opacity slider until you get the desired result.
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Above left was a picture converted to black and white using LAB colour mode. It's a bit flat (no blacks) so the background layer was duplicated and the blending mode of the upper layer set to multiply. This turned out to be too dark and so the opacity was reduced to 65%. |
A few last important points
If possible shoot in RAW mode on your camera. Not only does this give you the added advantage of being able to work at 16-bit colour depth (which can make the effects of black and white filters more accurate), but it allows you to change the white balance, and this can have a knock-on effect on the quality of your black and white image.
When blending the different colours, remember that the blue channel will have the most noise in it. It is therefore a good idea to try and use as little of the blue channel as possible in the black and white conversion if you want to keep noise to a minimum.
When colour clipping occurs in individual channels, it is not usually too much of an issue with colour photographs. However if you convert to black and white, and base the conversion on a channel that has clipped highlights, then this can become very obvious in the black and white image.
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