Apply the Channel Mixer to the 'Monochrome' Layer to create a high contrast Monochrome image.
- Make sure the 'Monochrome' layer is selected
- Menu 'Image -> Adjust -> Channel Mixer...'
- Tick the 'Monochrome' box at the bottom left of the Channel Mixer
- Play with the sliders to get a high contrast black and white image. I used 200% Red, -50% Blue, -50% Green and 0% Constant. A rule of thumb is that all four numbers should add up to 100%
We are using the channel mixer to achieve the same effect as placing a strong Red filter over the camera lens when exposing a black and white film.
The use of negative numbers in the Channel Mixer means that we have created a filter that cannot exist in the real world. Negative numbers are like using Black (subtractive) light as opposed to White (additive)light.
If the Monochrome image is your goal, be careful as negative numbers usually make the Monochrome image look unnatural. However, negative numbers work particularly well in conjunction with the remaining steps of this technique.
These Channel Mixer values mean that the Monochrome image is made up by starting with twice as much red as was in the original image, subtracting some blue and finally subtracting some green. Any colour with more than 50% Red will result in White. Any colour with Blue or Green in it will appear darker than if the Blue or Green was not present.