Photoshop for beginners. Selections by Channels
Channels in Photoshop are grayscale images that store different types of information:
Color information channels are created automatically when a new image is opened. The number of channels created is determined by the color mode of the image. For example, an RGB image has channels for each color (red, green, and blue) plus a composite channel used for image editing.
Alpha channels store selections as grayscale images. By adding alpha channels, masks can be created and stored that allow certain parts of the image to be processed or protected.
So How to make selections using channels in Photoshop? There is a lot of ways how to make selections in Photoshop. Using Channels is one of the methods of how to make very accurate selections in Photoshop, especially when you have complex subject to be selected. To see the channels click next to the Layers and Paths tabs here :
If you don't see the Channels tab go to Window->Channels
Now go through all channels (Red, Green, and Blue) and find one with the highest contrast of the subject against the background.
In my case, it is the Blue channel.
Make a copy of Blue Channel.
Click on it and duplicate it by dragging it to the New channel button located in the bottom right corner. This step is necessary to continue working with it. If we did not make a copy of the blue channel and we would continue working directly with the original, it would increase the contrast of the blue channel and change the original colors of the photo.
Select this new copy of Blue Channel and make a selection by Ctrl+Click on this channel. Now you have the selection loaded. You can now refine the channel by Image adjustment -> Levels to whiten the whites and darken the darks. Afterward, you can refine the contrast even more by painting with a brush in Overlay mode:
When the channel is well refined, you have to invert it, because we want the object to be white, as the selection process in Photoshop works like it is selected white part of the image.
Ctrl + Click on the channel to load the final selection
Deselect/make invisible the edited channel and select/make visible all basic channels: RGB, Red, Green, Blue
Click on the layer, where is the original image: subject on the background and hit Ctrl + J
Now you have separated subject on the new layer.
So you can make the original layer invisible and now you will see final selected object cut out on new background - prepared/created before and located under the original image.
Channels are often used as a repository of selections. Let's show it in a simple example. Open any image and create a new selection. You can use any selection tool: Lasso tool, Quick selection tool, Magic wand tool, Marquee tool, or even Pen tool. When you create the selection itself, click Tab Channels and then click Save Selection as a channel in the bottom sheet. When you click, a new channel is created automatically. Alpha channel is a black and white expression of our selection. This way, we can store more selections and reuse them at any time in the future. To use this saved selection, do Ctrl-click on the appropriate Alpha channel, and the selection will load automatically.
Channel usage is huge and powerful
It is convenient you can combine multiple channels into one complex channel, which represents a selection composed of multiple sub-selections.
For example, imagine a situation where you have to create a complex selection. This selection consists of several parts such as the head, hair, body, and other parts of the image. Each of these parts may be selected by another technique. For example, the selection of hair will be made using channels. Please select the channel with the highest contrast and adjust it. We use adjustments like Levels, Curves, and so on.
For final enhancement, we can paint with a brush in Overlay mode to increase hair contrast to the background. But this will only be one part of the selection, so we save it as Alpha channel 1. Then we create a selection of another part of the body or head. These parts can be selected using the Quick Selection tool or the Lasso tool. The selections created this way will be saved as other Alpha channels.
Once we have all the partial selections made and saved as Alpha channels, do the following: do Ctrl + Click on the first of the saved Alpha channels and create a new selection. Then press Shift + Ctrl + Click to add more Alpha channels. In this way, we create a complex selection that we can save as a brand new alpha channel and use it in the future.
Another Channels usage
Channels can also be used for other purposes, such as removing a color cast. A typical example is a portrait photo where a color cast is visible in the skin area of the face. Quite often, there are blue or yellow colorcast. This drawback can be remedied using channels. In this case, create a new adjustment layer - Curves and change the default RGB channel to Blue channel. RGB channel represents a composite of all three color channels Red, Green, and Blue. But we need to adjust the blue color cast and therefore choose Blue channel. The next step is to drag the curve on the blue channel down to add a yellow tone as needed. Similarly, this method can be applied using the Levels adjustment layer. The setting is similar to changing the position of the gray slider instead of changing the curve.
Advanced mask enhancement and selection
Often there is a situation when we need to increase the contrast of the selected object against the background. Then, the selection is better applied to the object. Let's choose a mask or channel that will be the source of selection. Select a soft brush and adjust its size so that it accurately paints along the edge of the object. I use setting with lower Flow parameter and gradually build up the painting. It is imperative to set the Overlay mode before painting. This mode ensures the contrast of black or white - depending on the specific situation. The gradual painting thus increases the contrast of the selected object, and we obtain a more accurate selection.