Black and white conversions.

 

November 2011-

 Recently there has been an upsurge of interest in reproducing pictures in Black and White, or as I prefer to use the term monochrome.

 In film days you could choose to use a colour or Black and White film. The black and White film would be Panchromatic, i.e. sensitive to all colours which meant that each colour would be rendered a different tone of grey. It was possible to exercise some control of the final tones by the use of colour filters over the lens when taking the photograph.

 I have already placed a thread about this which might be read before continuing with this article.

 

http://www.myfinepix.pl/forum/33538/365071

 

With many digital cameras it is possible to set it to take monochrome or perhaps Sepia images. The results may vary depending on the camera and the software used. Whatever the result you will have little further control of the tones in the image.

 Using a colour image and converting to monochrome using the right software can restore the same type of control of the grey tones, just as could be done with film, and for the same reasons.

For many converting to monochrome using the ‘Greyscale’ is simple and considered enough but once done the tones are fixed because all the colour information has been removed. Increasing contrast and brightness may appear to improve the picture but it has not actually changed the tonal shade, just made it lighter or darker. This may help to separate the tones but perhaps at the loss of some detail.

The task is to convert to monochrome without losing the colour information in the image. How this is done will depend on the software used.

I only have experience of Photoshop and all the illustrations below were produced using Adobe Photoshop CS5.

To make the conversions I use the Channel mixer. This tool has been in all versions of PS since v5 which was produced in the 1990s. I understand that it may not be in versions of Adobe Elements. CS5 has a more sophisticated monochrome palette but the channel mixer is more common in other software and easier to demonstrate.

 

Picture of channel mixer.

 You will observe it has three sliders. Red, Green and Blue. The values will relate to the image on the screen which will vary depending on the nature and colour of it.

The bar at the bottom labelled constant can be ignored.

At the bottom left corner is a tick box marked mono. When this is checked the image converts to mono in a sort of ‘greyscale’. Note the slider values change and are defaulted to Red +40, Green +40 and Blue +20Which add up to 100.

 N.B.

When changing the values the total should always be around the 100 mark, allowing for plus and minus figures.

 When using this method with a photograph the movements can be quite small and still make a considerable difference. I have used a flat image of colour only to illustrate what happens.

A blue panel with coloured text with the text colour in each line so that you can keep track of the tonal changes.

 

 Picture of Base image.

 This is the ‘Greyscale image. Before this can be activated PS adds a warning that doing so will remove the colour information and suggests to use other methods.

 

 Picture of greyscale .

 

 Picture of warning.

 

Choose channel mixer instead and click the mono check box.

 

 Picture of image with channel mixer in the mono position.

Now you can play with the sliders and see what happens, but remember to keep the total to around 100.

 

  Red +50  Green +50  Blue 0

 Red 0  Green +100  Blue 0

 

 Red 0  Green 0  Blue +100

 

With a colour image the changes can not be so dramatic unless you want an unusual image which may no longer look natural.

For these illustrations I have used three peppers, red, green and yellow. In the background there are three cards, black, white and grey. The grey is a Kodak 18% grey card to use as a reference point. The basic image was neutralised on the grey card. The black was the only piece of card I had and it has picked up some light reflections, however it should serve the purpose.

First note how the cards have picked up colour reflections from the brown paper at the base. It indicates just one of the problems of getting colours right in such photographs.

In the following series I have indicated the colour slider settings. Note the tonal changes of the peppers. With practice you can get the relationship that seems correct. For instance, the yellow pepper would normally be the lightest. With the other two which should be the darkest? You can change the tonal values by using the sliders.

The values I have chosen are random and I do not suggest that one is correct. That is for you to decide. Using this method you have a choice.

 

N.B.

Take note of the neutral grey cards in the background. As long as you keep that total number at 100, the tone should not change very much   with this method. In this case the mono conversion has lightened the overall image. However the contrast and brightness remain the same. You can still change this later if it is appropriate, but if the original image was correctly exposed and prepared it should need very little.

You can not do this by trying to adjust a greyscale image using contrast and brightness. Such methods will always change the relationship of the neutral tones.

 

Try it yourself.

 

 Base colour

 

 

 Channel mixer in mono.

 

 Red 80  Green 20  Blue 0

 

 

 Red 0  Green 80  Blue20

 

 

 Red 0  Green 100  Blue 0

 

  Red 100  Green 0  Blue 0

 

  Red 0  Green 0  Blue 100.

 

The principle is as follows.

 A Red filter will lighten Red and darken Cyan.

A Green filter will lighten Green and darken Magenta.

A Blue filter will lighten Blue and darken Yellow.

 The degree of change depends on how much of each filter you use.

 Also remember that a filter will affect every pixel containing the filter colour, so be sure to examine the image for any strange effects. In the illustrations above you may have noticed that the brown paper also changes tone depending on what filter was used. Brown is often made up of all three primary colours so will be affected by every filter in some way.

 I hope you will be encouraged to experiment with this technique for more satisfactory results when you convert a colour image to monochrome.