What are Photoshop Channels?

The use of Photoshop channels is very useful when trying to make complex selections in Photoshop. 

Every image in Photoshop is made of three colours, red, green and blue. Most commonly abbreviated as RGB. This colour mode is used for all monitors and screens as every pixel is produced using a mix of these three colours.

The Photoshop channels tab provides a visual representation of how much Red, Green and Blue are in each image. The amount of each colour is represented by shades from white to black. Black is found where there is the least amount of red, green and blue. White is found where there is the most amount of red, green and blue. 

Let’s use an example picture of a red car.

red car photoshop

As you can see if we select the car layer and then move over to the channels tab and look at the red channel you can see it’s almost pure white meaning this part of the image containers the most red. Which makes perfect sense as the car is obviously red.

red channel selected

Let’s use another example like this tree, let’s move over to the channels again and this time select the green channel. We can clearly see as expected the greenest parts of the tree are almost white.

photoshop green channel

Using Photoshop Channels is a really good way to find colours within any image. It can sometimes be surprising the number of colours found within the image. You would expect this image of a tree to contain a lot of green however not much of the image is actually pure green but a mix of green red and blue. Therefore a lot of the image is just various shades of grey.

photoshop channels

Using channels to replace a sky in Photoshop.

We can use channels to make selections in Photoshop to either replace a sky, remove a background or make tricky selections. I mention a few ways to make selections in photoshop in my post Making Complex Selections In Photoshop.

In the video, I remove a white (ish) sky in Photoshop and replace it with a sunset. Let’s go over the steps.

  1. Select the layer with the image on and move over to channels. If you can’t find channels make sure it is selected under Window > Channels.
  2. Look through each channel and decide which provides the most contrast. The goal here is to find the channel that has the best contrast. Dark subject and White background. (or vice versa) the better the contrast the better the selection when we come to use a layer mask.
  3. Duplicate the channel with the most contrast by dragging it over the new layer icon found at the bottom of the Layers panel.
  4. Using the brush tool, paint over the black areas with pure black. Paint over the white areas with pure white. The idea of this is to give even more contrast to the image making it easier to create a mask later and produce an accurate selection.
  5. Make sure the duplicated channel is selected and press Ctrl + left click to create the marching ants.
  6. Move back to the layers tab and press the mask button found at the bottom of the Layers panel.
  7. Press Ctrl + I to invert the mask to show and hide either the subject or background respectively.

What is a layer mask?

A layer mask allows us to show and hide parts of an image. When creating a mask if it is completely black, none of the layer is visible. If the mask is white, all of the image is visible. 

By making a selection based on channels we can use black and white to separate parts of the image. In the video example, we make the sky as white as possible and the subject as black as possible.

When we create a mask based on this selection it hides the foreground. (the totally black areas) this is fine we can invert this selection by pressing Ctrl + I. You can toggle this and invert again depending on whether you want to hide the foreground or background.

Once we have our image with a transparent sky this makes it really easy to drop another sky into Photoshop and drop it behind the foreground. Because we have a mask. The black areas will hide the original sky and show the layer behind it. In this case the new sky image.

Once you have your sky in the background use Ctrl + T to drag and place the sky to fit the scene. 

In the video example, the foreground was too light. After all, this is now a sunset so the foreground should be a lot darker and in shadow. If you locate the adjustment layers icon at the bottom of the Layers panel select “Brightness and contrast” make your changes to the light and darkness until it looks right. Don’t forget to “clip” the adjustment layer to the foreground layer underneath or this brightness change will affect all parts of the image. 

new mask and layer adjustment icons

We can clip the layer to the mask underneath by hovering with the mouse around the bottom of the layer and Alt + Left click. Or you can right-click on the layer and select “Create clipping mask”

I hope you enjoyed the video above. The original speed art can be found on my Instagram page @clicky_rick.

Thanks for watching and reading.

Rick