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In this movie I would like to expand our understanding of grayscale values in Channels. In previous movies we talked about the basic building blocks of a digital image, what does a scanner or a digital camera capture, we saw that it captures pixels. We talked about the fact that depending upon the scan mode that you choose you'll end up with single or multiple channels and you can have black-and-white simple black-and-white or grayscale values in pixels that your scanner or digital camera captures. And what I'd like to do here is develop that whole concept of grayscale value in channels and that number we actually put in those grayscale values.
So I have zoomed in here on this Blue- Green cape and it's very, very colorful image, and just to review when you capture a "color image" what the scanner or digital camera actually captures is three grayscale channels that we call Red, Green, and Blue, but as we see here they are really nothing, but grayscale, because that's all a digital camera or digital scanner can capture. And where does this color come from? Remember that all colors created by output devices. In this case the monitor on which you are viewing this image actually applies Red, Green, and Blue colors to these grayscale pixels and the amount of Red, Green, and Blue that are size of the pixels depends upon the grayscale value that's on the Red, the Green, and the Blue channel.
So let's take a look at an individual pixel and here I am going to use my Info tool in Photoshop, that's the I for Info tool, and I am setting a Point Sample, so I am just measuring one pixel at a time. Normally when we're scanning or correcting images we'll do an average number of pixels, but in this case I just want to look at individual pixels. So I am going to zoom in just a little bit more. I see you can really see that we're just looking at one pixel. Now look at the grayscale value of that pixel, we'll do that by looking at their, remember, "color image" RGB values that we see over here, so when I look at the Info panel, the Red is 115, the Green is 140, and the Blue is 137.
Now with these grayscale values going to scale of 0 to 255 where 0 is Black and 255 is pure White, and we look at the ratio of these numbers, look at the Green and the Blue is higher than the Red which certainly makes sense, right, because this is a Green, Blue cape if you will. But what do these numbers actually mean? I am going to go through these three channels. I am just going to do it from my keyboard shortcuts. I am going to use Command or Ctrl+3, 4, and 5, as you see in the Channels panel, so that I don't move my tool from looking at that one pixel.
So I am going go to the Red channel and look at the Red value in the Info panel right after. It's at 115. Notice when I activate just the Red panel notice the number is 115. Let's go back to the RGB. Now the Green Channel is 140, so if we activate the Green Channel it's 140, back to RGB view, Blue is 137, guess what, when we go to just the Blue Channel everything is 137. So when you're looking at the Red, Green, and Blue values what we're really seeing is the grayscale value in each of those channels. The reason why this is so important to really understand is that when we're going to be controlling our scanners, we're actually going to be controlling the grayscale values that make up these RGB images on each of the three channels.
So this is on a scale of 0 to 255 where 255 is pure white, 0 is pure black, means the absence of that color. In as we have here in this Green, Blue image, the Green, Blue values will be higher than the Red because there is more Green and Blue than there is Red in this image. So it's all grayscale values that we're going to be capturing, editing, and manipulating during the scan process.
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