PhotoImpact Tutorials: Convert Colour Photos to Black and White

Convert Colour Photos to Black and White

There are a number of ways that colour photos can be changed to black and white with image editing software. The easiest options are converting a file to Greyscale, or using the Hue and Saturation tool to desaturate an image. Although these options are quick and easy, PhotoImpact's Calculation Tool often gives a better final image.


Digital Black and White
Although colour photography is very popular today, photographs can often look equally good, sometimes better, in black and white. Portraits, buildings, flowers and landscapes are just some of the subjects to which black and white is suited. So, how can you change colour images into black and white? With digital photography, there are number of ways to do this.
Digital camera files store images in three separate colour channels, namely Red, Green and Blue (RGB). By mixing these three colours together, millons of different tonal ranges are possible. Image editing applications such as PhotoImpact allow two of these channels to be discarded, leaving a single channel known as a Greyscale file. To change a file from RGB to Greyscale, select Format from the Main toolbar, then Data Type and Greyscale (8 bit). Alternatively, click the RGB icon in the bottom right hand corner of the application screen (shown right), and select Greyscale. Ensure the Create New Image option is checked (see right) so your original image remains safe. This will create a new black and white version of your colour photograph which can be saved separately from the original.
This method is quick, and often produces acceptable results, but the user has no control over the end result as its produced automatically by the software. An example of how colours look after conversion to Greyscale is shown below. The image shown left was produced by converting a RGB file to Greyscale. Blue in the original image has changed to a dark tone in the Greyscale version, with red showing as a midtone, and green and yellow becoming progressively lighter. Colours in the original that have the same brightness and saturation show as different tones in the Greyscale version, so red, yellow and blue are still clearly distinguished from each other.
One minor disadvantage of Greyscale files is that they cannot be toned with another colour (for example, blue), but this is easily rectified by changing the Greyscale file to RGB format. When this is done, PhotoImpact's colour editing tools can be applied to the image in the usual way.
Reducing Saturation Instead of changing the file type to Greyscale, its possible to retain the RGB format, and remove colour by using the Hue and Saturation tool. To open the Hue and Saturation dialog box, click Format on the main menu, then select Hue and Saturation (see left). If you want to retain the colour version of an image, select Duplicate from the Edit menu, then work on that instead of the original.
When the Hue and Saturation dialog box has opened (shown right), moving the Saturation slider to -100 removes colour from the image.
Unlike Greyscale conversion, colours of the same brightness and saturation have the same tone of grey when the desaturate method is used. This can be seen in the colour chart (below, left) where red, yellow and blue appear the same tone, rather than differently. Compare this with the Greyscale method colour chart (below, right).
Calculation Tool
The third, and most versatile, option on PhotoImpact for converting colour photos to black and white is the Calculation Tool. As mentioned earlier, digital camera files store images in three separate colour channels (Red, Green and Blue). The Calculation Tool can separate these channels, or merge them together using blending modes. The Calculation Tool can be opened by selecting Calculation from the Format menu. The dialog box shown below then appears. Select a channel from the Foreground pull down menu, then click OK. This opens a new file - still in RGB format - which can be saved or edited further as required.

Red, Green and Blue Channels
The images below show the original colour photo, and the Red, Green and Blue channel files produced by the Calculation Tool. All of these produce reasonable results, although the Red and Green channels generally tend to be the best. The Blue channel has a tendency to have more Noise (the digital equivalent of film grain) than the Red and Green channels, so is best avoided if you wish to minimise this. The results are essentially the same as would be obtained from using coloured filters with black and white film photography. For example, the red channel translates warm colours such as red or orange into light tones, and cold colours such as blue or green into dark tones. A single channel file may be all thats necessary in terms of converting a colour photograph into black and white, but if these alone do not produce the desired result, then further options are available by combining channels, and using blending modes.
Original (far right) and red channel (right) images.
Green channel (far right) and blue channel (right) images.
Combining Channels
Channels can be combined by selecting the channels you wish to use in the Foreground and Background pull down menus. The resulting output is previewed in the right hand side of the dialog box.

Further options can be produced with the Mask option, and selecting a blending mode from the Operation menu. Some blending mode options will produce awful results, but others will usually produce interesting, and often good quality results. The final image of the King Vulture was produced using the Red and Green channels, with a Green Mask, and the blending mode set to Inverse of Multiply.
Comparison Of Greyscale, Desaturation and Calculation Tool Results
A comparsion of black and white files produced by the methods discussed above are shown below. All three methods produced reasonable results, but the Calculation Tool produced an image with a better tonal range than the Greyscale and Desaturation methods, and distinguished more clearly between the warm coloured orange areas around the birds neck, face and beak.
It may sometimes be necessary to use additional editing tools on the image before a final version is produced. If this is the case, then Levels, Tone Map, and the Burn and Dodge tools will probably give your black and white images any finishing touches they may need.
		Finishing Touches To complete my black and white image, I made the background a little darker. To do this, I copied the Calculation Tool output image, and pasted it as a new layer object. I changed the blending mode of the new layer from Normal to Multiply, then reduced opactity to 50%. Finally, the Object Paint Eraser Tool was used to delete the area covering the bird on the layer copy, revealing the base image underneath.

Posted by Webmaster at July 27, 2005 07:47 PM