Tutorial: Using the Channel Mixer for B&W Conversion

[Trevor Ash]

Part 1 of 2

Photo 1: The original image.

If you've never gone to the channels palette now is the time to start becoming familiar with it. Every RGB image is comprised of three channels of information. The red channel, the green channel, and the blue channel. For an 8 bit image each separate color channel is represented as an intensity value from 0 to 255. When you look at each color channel separately in the channel palette window it's showing you how much of that color is at each part in the image by representing it as a lightness value from 0 to 255. There's actually an option somewhere in Photoshop that lets you display it in the color of the channel instead of levels of grey but that's not the best method for most.

When looking at the RGB channel it just represents the composite of all three channels.

When we look at each channel individually we start to see which channels have "Interesting" information in them. For example let's look at the red channel...

Photo 2: This is the red channel. Notice how bright the center of the flower is. That means that there's a lot of red in that part of the image probably in the range of 200 and greater (remember we're looking at levels from 0 which means no red to 255 which means the max amount of red possible).

Photo 3: This is the green channel. Notice how dark the ladybug shell became. This means that there is much less green than red in this area of the photo. Due to the middle grey tones in the rest of the image you can conclude that there is an average amount of green (probably around 120 or so) in the rest of the photo.

Photo 4: This is the blue channel. Notice how extremely dark the center of the flower became. The ladybug shell also became very dark. This means that there is little to no blue in those parts of the photo. The flower petals have some blue in them, probably due to reflections from the sky or just color casts from other soruces.

Hopefully I've now taught you something about channels. I'll post the part about actually using the channel mixer next.