Last week I discussed how to create a manual selection using the Quick Mask Mode in Photoshop. Which can be quite time consuming. This week I will talk about creating fast and accurate selections by using the Channels in Photoshop.
update November 13, 2017: you can save yourself all the trouble learning this technique in this tutorial and the other selection tutorials and at the same time save a lot of time and be more accurate by just creating selections with the new Quick Mask Pro panel.
Step 1: The Red, Green and Blue channels
Channels is one of the many tools I use for creating selections. You can make a perfectly fine selection literally in seconds, depending on your image and the complexity of the subject: some pictures work better than others. For this tutorial I am using an image by Andreas Thell. Let’s say I want to select just the flower. If I did this manually, it would take a good amount of time.
Instead of doing a manual selection, I’m going to use Channels. You can find your Channels on the rightside, next to Layers. You want to find the channel that gives the greatest contrast between subject and background. You can view a Channel by clicking on it. Don’t click on the eye, but on the words (i.e. click on Red).
The Red Channel gives a pretty good contrast.
The Green Channel looks good too.
In this case however, the Blue Channel is definitely the winner.
Step 2: duplicate the Channel
Now that you have found the Channel that gives the biggest contrast between subject and backgroud, duplicate that Channel. We don’t want to mess with the original Channels. Simply right click on the Channel you want to duplicate and select Duplicate. In this case I select and duplicate the Blue Channel.
This duplicate channel is actually a selection. You can go to Select, Load Selection and load Blue copy. But we don’t want to load the selection, so press CMD+D or CTRL+D to deselect. This duplicate channel is also a mask. White reveals, black conceals and the greytones are a bit of both. Greytones in a mask can affect an image, how much it affects the image is dependent of the value of the tone. It’s best if the mask consists of only pure blacks and pure whites.
Step 3: adjusting the mask
So, how do we get a completely black and white mask? One option is to just paint it with a brush. But an easier way is to use Levels or Curves. Make sure you have selected the Blue copy. If other Channels are selected, press the eye in front of the Channel to turn them off. Now, once you have selected the Blue Copy press CMD+M or CTRL+M to use Curves or press CMD+L or CTRL+L to use Levels. I prefer to use Levels.
Now simply move the sliders untill you have reached the wanted result.
The selection is now done, you can load it under Select, Load Selection, Blue Copy.
The flower was a relatively easy example. However, you can use this technique also on more complex images. Architectural photography images in particularly work great, because of the sharp lines and the contrast between the buildings and the sky.
You might be tempted to use the Quick Selection Tool to select the buildings or the sky. In some cases that might work great.
Channels work great when there is a clear contrast between subject and background. Especially architectural images work great.
You can also use Channels on even more complex scenes, but often you will need to refine the mask using other tools.
Masking out the sky doesn’t look like an easy job. There are a bunch of trees and a whole lot of cables. I can get a good selection by using Channels, but it requires a slightly different approach. This is something I’ll discuss another week.