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Understanding Histogram

Lesson 31 from: Photoshop for Beginners: Essential Training

Mark Wallace

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Lesson Info

31. Understanding Histogram

Histograms are an essential tool for understanding the exposure levels in your image. In this section, we'll go over the basics of histograms and how to use them.
Next Lesson: Adjusting Curves


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Understanding Histogram

let's talk about history grams and why they are very important to understand so that they can help us make adjustments in Photoshop. Now, if we zip over into Photoshop right now I have this image that I've loaded in Montana dot PSD. You can do that for yourself and to do this so we can see exactly what's going on. I'm gonna drag the hissed a gram right over here and so you can see the history graham here and you can still see me up in the corner of the window here. Now what we're gonna do here is to understand how this works. I can zoom into this image here and you can see that we have this little graph that's showing us the exposure values of this image. Now to understand how this works. Before we talk about photography, let's just take a step back and talk about what hissed a grams are because they're used not just in photography and Photoshop, but they're used across all kinds of statistical analysis. And so let me show you what they are. They're just a distribution of values across...

the scale. So let's think about elementary school and a classroom of 10 kids. And so let's say those 10 kids all take a test and they all get different grades. Now, some of those kids are sitting in the front row, one of them maybe gets an A. And one of the kids in the back row gets an A. There's some kids that get Bs and CS and Ds and a couple that get an F. And what we don't do is we don't take a chart and show those kids where they were sitting in the room and what grades they got. That's not what we do. We just make a chart like this. This is History Graham, it is a distribution of values across the scale. So two of these kids got an A. And three of them got to be and there's some seasoned Ds and Fs. So it doesn't matter where they're sitting in the classroom that doesn't impact where they show up on this scale. And you're thinking of course that doesn't show up doesn't change where these show up on this scale. But that's something that can confuse you when you're talking about Photoshop and the history Graham and Photoshop. So let's go back over here to Photoshop and remember this once again. So here is our history Graham. I'm gonna zoom out really fast. And what we're looking at here is this instagram is showing us the distribution of luminosity values from the darkest to the brightest in our image. So if we look at this again, I'm gonna zoom in on this just a little bit and you can see over here on the left, this is showing us absolute black how many pixels are absolute black. And then as we go to the right or seeing how many pixels are dark gray and a little bit lighter gray. All the way to the middle of the image, which is middle gray sort of just gray and all the way over here on the right hand side would be absolute white. It's gonna show us the distribution of values. And one of the things that can be confusing is if you look at an image like this, the left side is dark and the right side is light and that corresponds to what this looks like. But remember it's like the kids in the classroom, it doesn't matter where the pixels are in the image, it's just showing a distribution of those pixel values. So we have a lot of dark values, a lot of gray and no white at all. Now to adjust our image, we can use the hissed a gram to help us understand the exposure. So let me show you how to do that. So I'm gonna close this hissed a gram window and we're gonna go over here to our layers palette and then I'm going to make a new adjustment layer called levels and right off the bat in the levels panel you see hissed a gram. So this hissed a gram is showing us again how many black pixels we have, how many gray pixels that we have and how many white pixels that we have but we don't have any white pixels in this image but what I can do is I can take this slider right here and I can say you know what I'm gonna bring this over and now what I want this to do is I want this to be the white area. This to be the gray area and this to be the black area and we look at our image, I'll close this. You can see we have a white, we have a middle gray, we have absolute black. That's what the levels help us do. We can change where the grays are, we can say these mid tone values. These gray values. I want them to be a little bit brighter, wow. Look at there's color in this image. Who knew or I want to make them a little bit darker. You can change where those mid tones are. Can change where the blacks are. You can do all of those things using these levels. Now there's many tools for adjusting the exposure and the luminosity of different values and almost all of them use the hissed a gram to help us understand where the values are in our image and let me show you something else. I'm gonna reset these levels here. So we go back all the way back to the normal. In fact I'm going to click this, this is going to reset everything. So we're back to where we started and I want to just show you something just so you understand that the distribution of values is not correspondent to where the images are in the or the pixels are in the image. So if we have our history graham here, it shows dark on the left, there's dark on the left, we have bright on the right, there's bright on the right. But watch this. If I go to this layer, can I say image adjustments and then what I'm going to do here is actually gonna say image rotation flip Kansas canvas horizontally. When I do that, that flips this image around and notice nothing changes. So we still have the brights over here on the left. The darks over here on the right, the hissed a gram is exactly the same. It doesn't matter what I do to this image, I can rotate it like this bank is gonna show the same thing. And so now we have this bright line right here because we have a white background, we have this transparent background but the rest of it is the same. So this hissed a gram is just showing us what's going on in the image regardless of the orientation of the image itself. And we're gonna be using it over and over again as we go forward, adjusting images. It's a great tool to understand and learn

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Ratings and Reviews


Mark did a great job at explaining things and going over them multiple times throughout the lessons. My only issue was that sometimes it went a little faster than I could keep up and I needed to rewind it a bit and start again. But from someone who has never worked in photoshop before I 100% recommend this class to anyone trying to learn.

Terri Schwartz

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