1.2 Curves Panel and Histogram

[MUSIC] Welcome back to using curves in Photoshop. In this lesson we'll talk about the curves panel and how to read the histogram. In Photoshop, curves can be applied through the image adjustments menu which is also activated by the keyboard shortcut of Ctrl+M. But more commonly they are applied by using a curves adjustment layer which can be added through the adjustments panel. In looking in the properties panel of the curves adjustment layer we see this graph, this is what's known as the histogram along with the curve that's overlaid on it, although right now this curve is a straight line it will become a curve later on. But before we get into that, I wanna talk about what this graph behind it means, what this histogram actually is. If you look at the image we have open over here, you'll notice that there's a high number of very white areas right here in the center with a decent amount of mid-tone pixels, and some shadow pixels, but if you look closely you may notice that none of these shadow pixels are 100% black. They all look very dark grey, they don't look fully black. With that in mind let's take a look at what the histogram is showing us here. The histogram really is just a bar chart of the brightness or luminous values of the image. On the far left is where we would see the black pixels being graphed. The far right is where we would see the white pixels being graphed. There's 256 levels of luminous values in between those. Looking at this image, the histogram shows us that there's really no fully black pixels. And that's what we observed over here as well. And if you think about one degree of grayness brighter than black, we also don't have much. Until we get about half way through this first little quadrant here. Now these are still very dark greys and we see that there's a large amount of those. That's also reflected in our observations of the photo. And that just carries on through to the far right which is where the white pixels are being graphed. So we see there's this thin line here. That means there is quite a few white pixels that's represented by this bright spot in the middle of the image. So really the best way to think about the histogram is that it is a bar chart. Showing the number of pixels that are black, the number of pixels that are these different degrees of gray, and the number of pixels that are fully white. And that makes a lot of sense when you're looking at a black and white image. But once color is introduced to the image, it's really the same thing. But it's measuring the luminous values of each pixel. And that's when it's showing the RGB or the composite channels. Now the channels can be isolated, through the different color channels. Which also measure the luminous values of that color. But for the most part, you'll be working with the curves on the composite channels. But the curves window is really an input output graph. That's why the curve in its default state, is this straight diagonal line. It's taking the luminous inputs of the image, that's the horizontal axis. And it's remapping them to the output. Which is the vertical axis. It's saying, take all the black pixels in this image and make them black. Take all the white pixels in this image and make them white. That's why we don't really see any difference in the image with the default state of the curves adjustment layer. Now that we've gone over what the histogram means, and what the curves panel is showing us, how do we use this? Well, that's the next lesson. Where we will talk about some of the most frequent and useful features of the curves panel.