To show the difference that changing the colour channels has on black and white images I needed to choose a photograph that had two or more strong contrasting colours (blue and green, yellow and blue, or green and red etc). This would allow me to clearly see which colours and areas of the image are affected by changing which slider on my black and white converter. In essence what this exercise is teaching me to do is heighten my awareness of what tones change and can be changed and to what degree once the image is out of the camera (while I am in the act of taking the photo). If I were using film, I would have used colour filters to achieve the same effect. However, as I am using a digital camera in RAW format I have all the channels of colour available to me to edit and manipulate within the processing software. It is an exercise similar in nature to one I have done for The Art of Photography recently that can be found here.
The image here of a drinks stand in Phnom Penh has red and green as strong contrasting colours as well as yellow and blue.
First of all I made a neutral black and white conversion with standard settings in Aperture. Here the tones are all very even with green, blue and red looking fairly similar in tone.
For this image I pushed the red slider to the maximum setting on the slider and reduced the green slider to the point where I still had a viewable image (just as the green umbrella lost detail). The red umbrella has almost disappeared in to the white background and the Coke stand has also paled significantly (although not as much as the umbrella). The yellow umbrella (similarly a warm colour like red) is also very pale. In the background the warm brown of the corrugated iron is also lighter in tone. Meanwhile the green umbrella (a cold colour opposing red in the colour wheel) is black and the foliage in the background has darkened in tone.
Here we see almost the opposite effect. The green umbrella has lightened and the red one is black (as are the Coke stands below it). However, the green is not a pale in tone as the red was in the previous image. The yellow umbrella is also slightly darker. The foliage in the back remains surprisingly similar to the previous image. This may be due to the massive range of greens present in the foliage and the green slider is only affecting the primary green, which happens (unsurprisingly) to be the colour of the umbrella. The blue tones have remained very constant in both images.
This exercise is a good lesson in remembering what to look for when the intent is to shoot for black and white. It also starts to show the flexibility of black and white in post-processing.