Tutorial 2: Channels.
I find that the channels in Photoshop are helpful, but I’ve never seen anyone but me using them. I use them to store my masks. Over the years I’ve asked people why they avoid the channels, and almost everyone has said that they simply don’t understand them. With this tutorial I will try to demystify Photoshop’s channels.
Looking at the channels can be a little intimidating when you don’t know what they are. Most people stumble upon them by accident and think, “That has something to do with printer separations. I don’t have anything to do with that, so I’ll avoid that part of Photoshop altogether.”. It’s true, the channels do store the color information of the file. Open an RGB file in Photoshop and look at the channels. You will see that all red information is stored in the Red channel. The Green and Blue channels store their relative color information. Convert the picture to CMYK (Image > Mode > CMYK) and look at the channels. If you sent the image away to be printed on a press, this is what the separations made for the press would look like. This is one of the reasons Photoshop became so popular so quickly it was inexpensive but could handle separations.
Clicking the eye icons will display the various channels. In this example we are viewing only the Magenta channel.
Clicking the eye icon next to CMYK will view the image in full color again.
The channels are really just sheets of alpha (transparency) information. Just about anything you can do to a grayscale image could be done to a channel. You can apply paint, dodge and burn, or clone on a channel. You can make new channels and use them to store masks. These new channels are added in a stack under the channels that contain the color information.
First, lets make a selection and save it as a new channel. This will let us use the selection again if we need it. Good imaging is all about making good masks, so you will probably want to save a mask you have spent time making. Create a shape with the Lasso.
Hey, I spent 5 seconds creating this shape with the Lasso. I wish I could save it and use the selection again.
Now that we have an active selection, go under the Select menu (at the top of the monitor), select Save Selection, and a dialog box will ask you to name the selection. I usually just hit the return key at this point. At first it may seem like nothing happened. Now deactivate the selection with key command Command - D. You may be used to thinking that the selection is now gone forever, but it has been saved and may be activated as a selection again. Go into the channels and you will see the selection you just saved. I tend to think of saved selections as masks. You can load the channel as an active selection by pressing the button at the bottom of the Channel’s Panel that looks like a dotted circle. Let your cursor hover above the button for a moment and it will identify itself as “Load channel as selection”. Pressing the button loads the channel’s grayscale information as your current selection. Saving and loading your selections are extremely useful.
Hallelujah! My selection has been saved! I can make it active again with the Load button at the bottom of the Channels Panel.
Now let’s make a new mask by painting on a new channel. There is a button at the bottom of the Channels Panel that looks like a piece of paper with a bent corner. Press it to create a new channel. You can now use Photoshop’s tools to create a mask as if you were working on any grayscale image. Use the paintbrush to make a white streak across the channel. Now load the channel as a selection, and the channel will be loaded as a perfect alpha representation of your painted streak. Painting with black acts as an eraser on a channel. The key command Command I will inverse the values of the selection so that the positive values become negative.
In this example we are painting with white on a new channel. If you need to see the photo under your mask as a guide,
you can click the eye icon next to the color image (in this case it’s named CMYK).
Saving Channels in your document a word of warning.
Creating new channels will make the file size of a Photoshop document larger. This happens because each new channel could contain as much data as the channels that contain the original color data. Think of it this way: if you are working in RGB and you save three new channels, in theory you could be making the file size of your document twice as large. If you are working on a CMYK image and you make a new channel, you could be adding another fourth of the file size to the file.
I hope that you now know a little more about Photoshop’s channels then you did a few moments ago. The channels are there to be used. Check them out.
David Phillips, May 2004.
Copyright © 2004, David Phillips. All rights reserved.
No part of this document may be reproduced without permission from the author.