This exercise is in order to learn how to use colour effectively in order to convert to black and white. I have taken the image below using the colours red, green, blue and yellow.
This shot is a conversion into Black and white without any adjustments.
I have then used photoshop CS4 in order to add colour filters to a series of shots. The first one I have increased the slider of the red and we note that the red becomes lighter in colour until white if we so desire. The red and similar colours will lighten in shade where as other colours will darken the darkening effect is more efficient in its complimentary colour. Red is complementary to green and so you will see the red filter has opposing effects on each.
I have repeated the process with each colour slider in CS4. The next photo is an increase in the green slider.
The result as we expect is the exact opposite to the above so the green filter has caused the green apple to become lighter in colour however its complimentary colour red is seen to become darker as we see with the red pepper.
In this case by using blue we can see how the blue background has become lighter however its complementary colour is Orange which is not present however we note a similar change in the yellow as it becomes darker.
Above the yellow slider has lightened the yellow pepper the blue background appears darker however the green has also lightened.
I can see how by using colour you could create the most stunning of Black and White images if used in the correct way.
Just to show how we can control to colour to create the maximum contrast in the items I have adjsuted the following shot.