Selections – Part 2 Advanced methods with Channels

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.

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.

Flower by Andreas Thell

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).

Channels

The Red Channel gives a pretty good contrast.

RGB Red Channel

The Green Channel looks good too.

Green Channel

In this case however, the Blue Channel is definitely the winner.

Blue Channel

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.

Duplicate Blue Channel

Blue copy

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.

Adjusting the mask using Levels

Now simply move the sliders untill you have reached the wanted result.

Adjusted mask with levels

This looks pretty good, however the middle of the flower is masked out and there are some white points on the lower right side that I need to take care of. Simply use a brush to clean it up.

Pollution around a black edge

If you need to clean up around the edge, you can simply use the Dodge or Burn Tool instead of a Brush. In this case I want to get rid of the grey spots around the edge. I use the Dodge Tool set to Highlights with a opacity somewhere between 50% and 80%. This way you won’t affect the edges if you go over them with the Dodge Tool, so you don’t have to be too careful.

Cleaning up around the edges

In an opposite situation you can use the Burn Tool set to Shadows to clean up around the edges fast and accurately.

Brush adjusted mask

This looks done.

RGB Channels

When you are done, click on RGB to exit and return to the regular view.

The selection is now done, you can load it under Select, Load Selection, Blue Copy.

Load your selection

Finished Selection

Creating this selection took me literally less than a minute.

Architectural images

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.

Color photo

You might be tempted to use the Quick Selection Tool to select the buildings or the sky. In some cases that might work great.

Quick Selection Mask

A mask created with just the Quick Selection Tool. It doesn’t look bad, but if you take a closer look the selection is nowhere near perfect.

Channels Mask

A mask created using Channels. Notice how much more subtle this mask is than the one created with the Quick Selection Tool.

Channels Mask Refined

The final mask that I refined a bit.

Conclusion

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.

Calatrava bridge

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.

Early stage

This is in an early stage of the mask using Channels. All the mid greys are going to be troublesome. Bringing in the Whites with Levels will dissolve the cables. Here I need to combine different techniques. This is something I will discuss in detail in part 4 of this series. But first I want to discuss the Pen Tool in part 3 next week.

Calatrava masked using channels

The end result. This took me about an hour using Channels and other tools combined. How? You will see that in part 4!

 

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  1. […] Beispiel für Auswahl mithilfe von Kanälen: Hier klicken […]

  2. […] on how to create selections in Photoshop with all kind of tools. You can read them here: part 1, part 2, part 3. In this tutorial I will cover the most essential part of handling selections: how to save […]

  3. […] absolute control over your selections, you  can combine the Pen Tool with the Quick Mask Mode and Channels. So, what is the Pen Tool? It’s basically nothing more than a tool to create either straight […]

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