For this exercise, take or choose and image which contains at least two strong contrasting colours, for example, Blue and Green, Yellow or Blue, Green and Red. Using the channel sliders or controls available in your software, create two opposite versions of the image in black and white.
In one, lighten the grayscale tone of one of the colours, and darken the tone of the contrasting colour as much as possible.
In the second version, perform the reverse.
One of the things you will find in this operation is that the channel sliders often affect areas of the image that you had not expected. This exercise will help in refining your sense of hue.
This exercise is better performed on a RAW image. That way, you have direct access to the original three channels.
To begin with, Make and save a ‘Default’ black and white version. Keep this as a reference. You will need to be familiar with the way the channel or colour sliders work, but the principle is straightforward, as part of the conversion procedure from colour to black and white, dragging each slider lightens or darkens the grey tone of that particular colour.
An example is, raising the red, will make any red areas in the original image become pale grey, even white. At the same time, this affects opposite (Complementary) colours, so raising red in an image with a blue sky, will darken the tone of the sky.
You should aim to produce two black and white versions with a strong difference in their tonal distribution. Write down what effect these different adjustments have on the creative quality of the image.
For this exercise, I decided to use an image I had taken whilst at the Kidderminster railway. I spotted the perfect first aid box which had bold red and green colouring. I used RAW for this.
I converted it to black and white.
Black and white:
The straight convert to black and white, has caused the red areas to become a dark grey, and the green area to become a lighter grey. The white writing also has a grey tint to it.
I took this image, then slid the Red slider down -60 and the Green slider up +60. I tried it to -100 +100, but it was extremely dark.
Red -60, Green +60:
The red colour has turned black, and the green has become grey. The white writing stands out and is very bold.
I then slid the Green slider down to -60 and the Red to +60.
Red +60, Green -60:
The opposite has happened with this image. The red has become grey and the green has become almost black. The white writing has a grey tint to it.
This exercise has shown that after converting an image to black and white, by altering a certain colour slider, can significantly change your image. It is a helpful tip, especially if you want to lighten or darken a certain colour/tone, without altering the entire image.
I prefer image 3, because I like the bold black tone. It is very striking. I would alter the image however, and I would make the Red a bit lighter so its not too black, just so I could sharpen the detail on the front area. I would darken the green area so it looks like the green in image 2, because how it is at the moment is too pale.