Okay, we are going to talk about color channels and that's why I have the Channels panel open. This is an RGB image, so we have three channels Red, Green, Blue. Were this a CMYK image, we would have, you guessed it, four channels, Cyan, Magenta, Yellow and Black, and of course, we have the composite channel which shows us the image with all of those color channels superimposed on each other, all of them turned on. I am going to undo that and revert it back to an RGB image.
If it were a grayscale image, it would have just one channel likewise with an Indexed Color image, likewise with the Bitmap image. LAB Color has three channels, lightness, the A channel and the B channel. But whatever color mode you are working with, you are working with channels and I am going to stay in RGB to explain this, I prefer working in the RGB color mode. That color channels store the information about the color of each pixel in your image, by which I mean this.
I am going to take a sample of a point in my image, I am in my eyedropper tool and to lock a sample point onto the image, I am going to hold down the Shift key and Click. This brings up my Info panel and my sample point is right there. Now that particular color, that sort of pinky color is made up of a combination of Red at level 199, Green at level 75 and Blue a level 125.
If I wanted to see what that would be in CMYK without even needing to convert to CMYK, switch that there, and it would be Cyan 4, Magenta 86, Yellow 23. In RGB our Brightness values are on the scale of 0 to 255 for each of our color channels. So 0 is Black, 255 is White, the higher the number, the brighter the value and when we add all these together, we get the resulting color.
If I move this sample around, that particular yellow right there is made up of 235 Black, 163 green. You may have heard of the notion of 24-bit color. Each all that color channels is made up of 8 bits, 256, 2 to the power 8. 8 bits times 3 is 24 bits, that's where 24-bit color comes from. You'll notice that when we look at the color channels, we are seeing them represented as grayscale values.
And it's actually the grayscale values, the brightness values that are more useful to us, than seeing the channels themselves in color. But conceptually it may be easier to see them in color. First let's see them in black-and-white how they look, and we can evaluate the channels individually by clicking on them or by using the keyboard shortcuts, and they are indicated right here. Command+3 for Red, Command+4 for Green, Command+5 for Blue, and we can see in this image that the red values are brighter, remember the colors in this image? It's a sort of pinky red. Isn't it? So that's why the red values are brighter.
There is Red, there is Green, and there is Blue. If we turn Green and Blue on together, we see what image would look like without any Red. Red and Green together, show how the image would look without any Blue. I am going to go back to my Composite channel now. Let's view the Color channels in color. I am going to come to my Preference, Interface and turn on this option, Show Color channels in Color. And then we actually see the Red in Red and the Green in Green and the Blue in Blue.
That's useful for understanding how they work, but actually we're more interested in a practical way with the gray values in the channel. So I am now going to turn that Preference back to how it was, so I'll press Command+K or Ctrl+K and then click on Interface, uncheck Show Color Channels in color. Now as well as that color channels, where there are two other types of channel that I am just going to mention very briefly, the second type is an alpha channel and that's what we have here.
An alpha channel is nothing more than a saved selection, there are numerous ways to get a save selection, presumably you would start off using your Selection tools and then come and click on this icon down here, or from the Select menu Save the Selection and that's an alpha channel. An alpha channel has only gray values in it. The third type of channel and the one that's seldom used and the one that I will be discussing in a later movie is I Spot Color channel, where in addition to a typical printing inks, Cyan, Magenta, Yellow and Black, or just Black, we can use Spot Colors chosen from a color matching system.
And this will expand our range of printing possibilities. But the most important thing to take away from this is that it's the color channels, the combination of the Red, the Green and the Blue, or if you are working with CMYK, the combination to Cyan, the Magenta, the Yellow and the Black, that give us the appearance of color and that's how our Composite channel shows us our image.
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