Converting a colour image to black and white .
If we simply remove colour, or shoot the scene with black and white film, or even set the camera to black and white, the problem is we have no control over where the tones will lie in relation to one another.
As you can see, once we simply remove colour, different colours appear similar .
This is not a problem with digital cameras. If we had shot the scene with black and white film, the same problem would have occurred. The reason is that we see the world not only with colours, but with varying brightness levels too. While being different colours, the cars are roughly the same brightness, so once colour is removed they all appear the same shade of grey. If you were shooting black and white film, you would use colour filters over the lens. For instance, a red filter would pass red light with almost no loss in brightness, but would block blue light quite severely, so the results would be the blue car being very dark and the red balls being very light. This is how photographers such as Ansel Adams got the rich, dark skies and bright white clouds.
The colour you want to darken is the opposite of the colour filter you should choose.
The same problems persist in digital photography however, as the first two images show. The solution lies in filtration, just as it did with black and white film, but this can obviously now be done digitally with the RAW file.
We open the RAW file in Adobe Camera RAW (the same controls are available in Lightroom or Capture One) and click on the “HSL/Greyscale” tab and check the “convert to greyscale” box.
In order to adjust the tones, we would adjust the colour channel sliders appropriately as per the colour wheel on page2. The only difference is that when adjusting digitally, we actually adjust the colour we want to change directly.
With film, if you wanted to darken blue, you would add a red filter. Digitally, if you want to darken blue, you lower the blue channel slider. It helps if you have a colour version to hand by which to judge this. As the red car appears brighter in colour (its not, its just a more vivid colour) we will lighten the red car by adjusting the red, purple and magenta channels (they’re a pinky/purplish red). We want to darken the blue car too; as blue is perceived to be the darkest colour, we’ll reduce this. We also need to darken the green grass, but its actually greener than blue, so the aqua channel was reduced as well as the green. This resulted in a greater separation of tones .
Create a black and white adjustment layer (see previous page). This will turn the image black and white, and give us the channel adjustment sliders. If we select “Luminosity” as the layer blend, colour is restored.
However, when we now adjust the channel sliders, we can see the levels for each channel being adjusted in colour. We can paint the areas of the B&W adjustment layer’s layer mask in black, by selecting the layer mask icon ,you can even add a saturation adjustment layer, and increase saturation on the green and yellow channels. These effects are subtle, but the difference can make it worthwhile.