Why not to shoot black and white in camera

November 18, 2007 by Daniel | Filed Under Photography, Photoshop, Tutorial 

Most digital cameras have the option of capturing black and white images directly in the camera. It can be a nice feature to have sometimes. But you can achive much better results by doing the conversion yourself.

Digital camera sensors do not capture b&w images, they capture color images with three channels, each describing the lumniosity of each of the colors red, green and blue. Consequently, there is always a conversion taking place when you make a b&w photo. The three channels must be made into one grayscale channel. If you let the camera do that for you, you give up all control of how it is done, and how much of each channel is used in the mix.

If you do it in post processing on the other hand, you have full control. One way is using the channel mixer. It can be applied as an adjustment layer.

Check the Monochrome checkbox and you will get a grayscale image. The sliders control how much of each channel is used. The total percentage should be around 100%, but can vary pretty much from image to image.

To demonstrate the difference I’m going to convert this image of a bright yellow leaf you saw at the beginning of the post.

If we choose the three color channels separately it looks like this.

Red: Green: Blue:

As you can see there is quite a bit of difference. In the red one the leaf is very bright, in the green the leaf has a nice texture but blends in too much with the background. In the blue channel the leaf is very dark and the background very bright.

If we convert this image using Image>Mode>Grayscale we get an image that looks like this:

This is about what you could expect to get from an in-camera b&w image. As you can see there is not much contrast between the leaf and the background. The image becomes hard to read and it looks really bad.

How would we use the information in the r,g,b channels to improve this image? We would like to have the texture from the green and the contrast from the red. The blue channel is useful in this case, because we can use it to darken the distracting background by adding a negative amount of it in the mix, without affecting the leaf much.

So above is my version using the channel mixer. Click here to see the settings I used: Channel mixer settings. Adding a simple curvers layer to get some more contrast I get this:

That’s a whole lot better than the first conversion if you ask me, although there is a finer gray scale in the previous version. It depends on what effect you want to archieve.

Changing the settings you can get very different results. Here is another version where I subtracted a bit more of the blue channel to almost remove the background completely:

You might notice this last image is pretty noisy in the background. As a rule of thumb, the blue channel is the noisiest one while the green is the least noisy and most detailed and the red is the most contrasty.

There are many other ways to convert to b&w than just the channel mixer, the “black & white” option in Photoshop cs3 is one.

Thanks for reading!

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