Photoshop channels are closely connected with the color modes of an image opened in Photoshop.
Depending on the color mode of the image, the channels palette will differ.
Let’s focus on the most often used color mode, which is RGB. It is the most used color mode when we edit images mainly for pc screen usage or online publishing.
As we use RGB color mode, we can see in the Channel tab, and there are three or actually four channels. Red, Green, and Blue channel. Well, there is one more, and that is the composite channel or, in other words, the channel with all colors combined.
So what these channels represent?
As it is evident from their names, RGB channels represent the intensity of a particular color. But how it works with colors because the channels are black & white? Well, the channels are displaying the strength of a specific color.
So, for example, the Red channel will display the intensity of the red color on the whole image. And the intensity is expressed by the intensity of the white color.
So if there is a black area o the red channel you see on that part of the image is zero amount of the red color. On the other hand, there is an entirely white part of the red channel. It will express there is a pure red color on the original image.
This white intensity itself is also equal to a numeric value that can be from 0 to 255. So zero is the image part with no red color, and 255 value expresses the part of the image with pure red color.
Photoshop channels and selections
Now you can ask what the photoshop channels can be used for? Well, they are very often used is in precise selections, masking, or background removal.
Let’s have a typical landscape or nature photograph with a beautiful blue sky. And we want to change or replace the sky with another sky. Sure, you could use the selection tool, magic wand, and so on to select the sky and mask it ore directly replace it with another sky of your choice.
Okay, but what if there are trees or another complicated object right on edge between the ground and the sky.
In such a case, it won’t be easy to make the selection using standard selection tools. And here come the channels very useful.
Let’s have a look at the blue channel. Make a copy of the blue channel. This is a general rule - when you want to change anything with the channels, make a copy and never edit the original channels directly.
So you can see the sky part of the image is on the blue channel almost white. And this is a good starting point for further editing or selecting the sky.
As you want to brighten the part of the sky on the channel copy, you can use Levels adjustment, for example.
So move the sliders to brighten the white parts and with the darks slider make the darks even darker and even completely black if possible. If it is not possible, and you see the edges become to disappear, do not go further with the Levels adjustment tool. Here we can use another tool to fine-tune the channel.
And it will be the brush tool. So select the brush tool, press D key to set the default Black and white colors for foreground and the background. And now the most important part: set the brush blending mode to OVERLAY.
Use the Brush tool to fine-tune
Now set the white color as your foreground color. Paint over the bright parts of the image to make it completely white. Be careful near the edges. Then switch the foreground color to black. Paint over the darks and make the darks completely black.
If there left some parts, for example, on the black side, grab the lasso tool and make the selection and fill it with black color.
Make the final selection
So now, we have our channel edited to the final stage, and now we will make the selection. It is straightforward. Just press Ctrl on PC or Cmd on Mac and while pressed click on the channel.
And it will make the selection. Do not forget that the selected part of the image is the white or bright part. So if needed, just invert the selection.
And now, you can make a mask to the image layer and mask in the desired sky from another image.
How to save and load selection using Photoshop channels
I am sure many of you have sometimes worked on a complicated mask or selection that consumed pretty much of your time.
To be sure not to lose the selection or be able to use it later, you can even save any selection in Photoshop. And guess what: you can do it using photoshop channels. Just go to Select->Save Selection, and a dialog box will appear.
Here you can choose whether you want to save it as a new channel in the current existing document. Another option is to save the selection as a completely new document with the so-called alpha channel bearing the selection information.
To load the selection is the process opposite. Again go to Select->Load selection and choose the channel. If needed, choose the document and the channel you have saved in the past.
There are even more sophisticated methods of creating masks and selections using the photoshop channels. For example, Luminosity masks are becoming very popular.
Luminosity masks are specific photoshop channels. You can have more of them for the particular luminosity of the image.
You can create basically three types of luminosity masks Brights, mid-tones, and darks. And to have more detailed coverage, you should create more of each. So practically, you create many Alpha channels. There are specialized products and photoshop add ons allowing you to create automatically the complex luminosity masks
Based on these channels, you can create very detailed and precise masks or selections that are based on the luminosity of particular image parts.
Luminosity masks are used by landscape fine art photographers to achieve very focused selections and then targeted effects to be applied.
Photoshop channels are powerful, mainly in the masking and selection process. There are more types of channels depending on what color mode you are working in.
For example, if you prepare the image for offset printing, you should use CMYK color mode. In this case, you will find five channels in the channel tab: Cyan, Magenta, Yellow, Black, and the composite channel.
All in all, if you cannot create a selection via traditional methods using the lasso tool, quick selection tool, magic wand, or color selection, the channels method comes in to help.