Channels 1Channels 1 What are channels, and why should you care? Because they give you the power to control the degree to which pixels are affected by everything you do. When you open any color image in Photoshop, each color in the image will be represented in the Channels palette by a color channel. For example, RGB images open with a Red, Blue, and Green channel, as well as a composite RGB channel. We’ll discuss them later. First let’s consider the channels you create by saving a selection, or clicking the New Channel button in the Channels palette.
Used for storing color, and alpha channels Grouped with the Layers, and Paths palettes
In the default arrangement, this one will be in the group at the bottom of your column of palettes. If the Channels palette is hidden behind the Layers, or Paths palettes, click on its title tab to bring it to the front, or choose Window > Show Channels.
Default channels in the Channels palette will be red, green, and blue if you are in RGB mode, or cyan, magenta, yellow, and black if you are in CMYK color mode.
You can turn channels on or off by clicking the eye icon next to their thumbnail. Turn all the color channels on or off at once by clicking the composite RGB, or CMYK channel’s eye icon.
You can do some very interesting color corrections, and image manipulations by editing individual color channels, but this is for experienced users, only.
The main use which the rest of us will find for channels is for saving selections. If you have spent a long time creating a perfect selection of a difficult subject, you should always save it as an alpha channel in case you need to use it again.
Alpha channels are masks that are saved in the Channels palette with your image file. Selections saved as alpha channels can be edited in the same way as quick masks. You can use any of the painting tools to add to the mask with black, or remove it with white. Gray will create a partial selection.
You can create alpha channels with the gradient tools that will allow a gradual blend of selected areas into nonselected areas when the channel is loaded as a selection.
In the illustration below, you can see the shortcut keys for each channel, listed at the right side of the palette.
To save a selection as a channel, choose Select > Save Selection. Accept the default options, and click OK. You can also save a selection by clicking the Save Selection button at the bottom of the Channels palette.
Please note that this entire palettes section has been updated from a Photoshop 6 version (which was updated from a 5.5 version). Wherever the palette is essentially the same as it was in 6, I have continued to use the screen capture illustrations made using that version. So if you notice cosmetic discrepancies in the illustrations, that's why. In all instances where features were added or changed, I have made new screen captures.
The illustration below shows the Channels palette with numbers added at the bottom for ID purposes.
The numbered icons are 1) Load Selection; this will load the selected Alpha channel as a selection outline 2) Save Selection; this will save the selection currently active in the image as an Alpha channel 3) New Channel will create a new, empty Alpha channel 4) the Trash, or delete button.
Shown below, left is the Channels palette’s options menu.
The Channels Options selection (which is grayed out in the menu illustrations) leads to a dialog box shown at right below, that will allow you to choose a different color for the masking overlay that appears when the Alpha channel is activated at the same time as the image color channels. The default color is a transparent red, but you can pick any color to replace it. You can also change the transparency of the mask color (not of the mask itself), and choose if you want the color to appear on the masked or unmasked portion of the image.
If you choose Split Channels, you can generate new grayscale documents from each single color channel. Each new document will include the color letter for the channel from which it came (R for red, B for blue, etc.). Then you can use Merge Channels to stick them all back together (if you want). First you'll be asked what Mode you want so use. Then, in the next dialog, you can decide which channel will go where.
Now do the following channels 1 tutorial These are called alpha channels. Alpha channels are saved masks. Masks are saved or stored selections. Selections are maps that tell Photoshop how much to apply color, effects, filters, or adjustments that you make while that selection is active. Understand that masks and selections are different forms of the same thing . Selections are temporary masks. Masks are stored selection maps. Alpha channels don’t show up in your image. They are stored selection maps which you can edit, and reuse as many times as you like. They are saved with the image so long as it is in Photoshop’s psd format. An alpha channel is a black and white ‘map’ of your color image. Where it is black, when loaded as a selection, it tells Photoshop, “leave these pixels unaffected by any changes.” Where it is white it tells Photoshop, “make these pixels 100 % affected by any color, filters, or adjustments applied.” Where it is gray, it tells Photoshop to affect those pixels in the same percentage as its shade. Lighter gray gets more affected; darker gray gets less affected. To show you that selections and masks are the same thing, try the following demonstration. Choose File > New to make a new white document. Create a new layer by clicking the New Layer button in the Layers palette. Make sure this new, empty layer is selected. Select the Type tool. In its options bar, choose the Masked Type tool (the T with a dotted outline, second from the left), set its options to Helvetica, Bold, 72 pt, and Strong (for anti-aliasing).
Type a capital A. With the letter’s selection outline active, choose Edit > Fill. Click the color square in the Fill dialog box to pick a color. I chose a bright red for my color; you can use black if you prefer. Next, go to the Channels palette. Click the New Channel button at the bottom of the palette. Your white document will turn completely black. This is simply the new channel which is a mask covering the entire image. Choose the Mask Type tool again with the same settings. Click on the black mask, and type a capital A. Choose Edit > Fill and pick White from the menu. Choose Select > Deselect, or press Ctrl-D to deselect the white A on the mask. In the Channels palette, with the new channel still selected (showing dark blue) click on the Load Selection button, or go to Select > Load Selection and choose Alpha 1 from the dialog box’s menu. Click on the composite RGB channel at the top of the Channels palette to make it active, and deselect the new alpha channel. Choose the Eyedropper in the toolbox and click on the first letter A you made to make its color your foreground color. Choose Edit > Fill and pick Foreground from the menu. Now, compare the two letters. They are identical. 
Just in case you’re still doubtful, here is a magnified view of the bottom of the two A’s shown above.
Ah, but this magnified view brings us to the next part of what masks and selections do. Notice that some of the pixels are neither red nor white, but are various shades of pink. Anti-aliasing was checked in the Type Mask tool’s options bar when the letters were made. This is an image effect. It is a form of instruction. It says “add some intermediate shades just here, and here”. In fact, it is even more precise than that. It says “at this pixel, add this exact shade, and at this one, add this particular shade.” Masks and selections are pixel maps telling Photoshop, How Much? for every single pixel. Let’s look at a close up of the mask at the enclosed part of the letter A, shown below
I’ve made a screen shot of an extremely magnified portion of the bottom right corner of the triangle, and numbered all the shades of gray. Remember, this is the mask, not the red image.
1. Pure white 2. 
3.
4.
5.
6.
7. Black Note that you are seeing RGB values since this is a screen capture, not the original mask. The mask would show only K, or black percentages as masks are grayscale, not RGB. When that mask was loaded as a selection, and filled with a color, I got the result shown below.
As you can see, the mask has provided pixel by pixel instruction for how much the color you added should affect the existing, base image (in this case, white) pixel’s colors. More here, less there.
Let’s look at a photograph. I have added a color gradient to the base of the image to help you see what is happening when I show you individual color channels.
I created a new channel by clicking on the New Channel button at the bottom of the Channels palette. The image was covered with the black of the new mask. I chose the Gradient tool in the toolbox, selected the Linear Gradient tool, picked the Black to White gradient in the tool’s options bar pop-up palette, and dragged from the left side of the mask to the right side, completely traversing the image. The result looked like this:
The Gradient tool is Used for adding, and editing gradient color blends Found at #22 in the Toolbar diagram
The gradient tool is grouped with the paint bucket in the toolbar; if it is hidden, click on the paint bucket and choose it from the pop-up menu.
The linear gradient is applied by dragging over the entire length of the area you are applying it to. The other four gradients are applied to the radius of the area, since the gradient will expand outward in all directions from the start point. The Linear gradient adds shades from where you first click to where you release the mouse button after dragging across the image.
The radial gradient, icon shown second from the left, above, applies shades in a circular pattern, radiating outward from the point where you first click. The line you drag is the radius of the circle of colors.
The colors applied by the angle gradient, icon shown center above, look like a cone, or Chinese hat, with the point at the top being the spot where you first click. Shades are applied in a counterclockwise spiral.
The reflected gradient, icon second from the right, looks like the linear gradient but with a mirror image gradient radiating in the opposite direction from the linear one where you have dragged with the pointer.
A diamond gradient looks like a starburst, or lens flare with distinct, shaded flare lines radiating from the point where you first click.
The gradient you have chosen, or created in the gradient edit dialog box [see second section below] is applied from the color shown on the left side of the gradient bar on the options palette, to the right. If you wish it applied in the other direction, check the Reverse box in the palette. All gradients will cover the entire layer with their colors. The area you drag over will show the gradient variations and the rest will have the end color without gradient. If you want the gradient applied only to a particular area, select it first, and apply the gradient within the selection by dragging across it. All gradients are applied with a transparency mask. You can turn it off by deselecting Transparency in the options palette, or edit it in the gradient editor [see second section below]. If you have problems with banding in your gradients (colors separating into stripes of different shades instead of making a smooth transition), try applying a small amount of noise with the Add Noise filter. Choose Filter > Noise > Add Noise. If you choose Edit > Fade immediately after using this tool, you can change the opacity and blend mode of the strokes you have just applied. After I used the gradient tool I clicked the composite RGB channel to select it, and deselect the alpha channel I just created. I then loaded the channel as a selection by choosing Select > Load Selection, or by clicking the Load Selection button in the Channels palette. With the gradient selection active, I chose Edit > Fill. I picked White from the menu and clicked OK. Note that if you try this, you will see that the ‘marching ants’ selection outline will contain exactly one half of the image, not all of it, even though the selection included all of the image. This is because the marching ants selection outline only includes pixels that are more than 50 % selected. The rest of the image was in fact selected, but in steadily decreasing amounts due to the gradient mask.
Here is what I got. As you can see, where the mask was lighter, the white fill color has been allowed to affect the base image to a greater degree. Where the mask was darker, it has allowed the white to affect the base image less.
A reading taken with the Eyedropper from exactly the center of the mask (not the image)
would show a reading in the Info palette like this:
Channel masks are created in Grayscale and K is the letter used for black. If you drag the Eyedropper across the gradient mask while watching the Info palette readings, you will understand that there are 255 degrees to which Photoshop can be told to affect each pixel with any colors, adjustments, or filters applied while a selection created from that mask is active.
The default setting for channels is to have black indicate the areas that are masked, or which would be excluded from a selection made from the mask. White indicates the areas that are not masked, and which will be included in the selection when the channel is loaded as a selection. However, you can reverse this order if you like. I have created a new channel mask on the photograph, this time creating various shapes with selection, and painting tools, and then filling them with white.
If I double click on the Alpha channel’s name in the Channels palette, its Channels Options dialog box will open.
If I choose the Selected Areas radio button, as shown, my mask will then display like this:
This is relevant because the latter is the way Photoshop displays color information in the CMYK color channels which automatically appear when you open a color image in that mode. Darker areas are where there is more of the color. Lighter areas are where there is less of the color. Either way, the selection which results when the channel is loaded as a selection is the same. I did that, then chose Select > Inverse to choose all areas other than the shapes I had drawn. I then chose Edit > Fill and chose Black from the menu. If you have the default colors in your toolbox colors boxes (with black as the foreground color), you can press Alt-Backspace to fill with the foreground color. Here is what I got. The selection edges are also shown.
The shapes were created with different tools which had different edge effects. I also added feathering to several, and anti-aliasing was selected for three of the forms.
Details are as follows: 1. Created with a large soft brush by stroking with white on the mask using the paintbrush tool. Detail below.
Created with the pencil tool by drawing with white on the mask. This tool makes hard edged strokes with no blend at the edges. Detail below
This was drawn be dragging a selection on the mask with the rectangular marquee tool. I had zero feathering set in its options bar, and the rectangular marquee tool does not use anti-aliasing. I filled the shape (on the mask) with white.
Same as number three, but this time I added a 3 pixel feather to the rectangular marquee tool’s options bar settings before dragging the selection on the mask. Detail below.
Ditto the above, but this time I used a ten pixel feather setting.
This one was a text outline selection created with the Type Mask tool in exactly the same way as the two red letters at the start of this tutorial. Shown below is a detail from the middle of the right side of the letter.
This is the letter D, created in the same way as the preceding letter A, but with a 2 pixel feather added to the selection after it was created. I chose Select > Feather and chose 2 pixels before I filled the shape with white on the mask. It didn’t show up well in the image, so I recreated the effect with a red letter on white.
This is a shape created on the mask with the Custom Shape tool. When using the Shape tools on a mask, the only option available for type is the Create Filled Region. I kept anti-aliasing checked in the options bar. The shape was filled with white on the mask.
I will repeat the same graphic information I showed you on page one for one of the mask shape outlines to make the point, once again, that the channels, and the masks they store are image maps. They tell Photoshop “How Much?” to affect the existing pixels with any new colors, adjustments, filters or effects that you add while a selection created from that mask is active. Look at the detail shown for item number four in the numbered graphic above. Here is the mask detail that created the (inverted) selection that was filled with black.
Here is a numbered graphic of that mask
1. Pure black. In the inverted selection, this area is 100 % affected by the colors added, in this case, black.
1. Pure white. Since I inverted the selection created from this mask, the base, or existing image pixels in these areas were 100 % unaffected by any changes made while the inverted selection was active.
To continue with this lesson click on the link below
Channels 1 B
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If you choose the Eyedropper, and drag it over the shades of gray, the Info palette will show the following results:
