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The most powerful and flexible way to adjust tones in an image is with Curves. Curves like Levels can be used to adjust brightness, contrast and even color in an image. But while Levels offer just three tonal controls, the Black, White and Gray sliders. With a Curves adjustment you can control up to 16 different tonal values with a single adjustment. I'm going to apply a Curves adjustment layer to this image to introduce you to the Curves Interface and show you how to use Curves for just one of its purposes to fix the exposure or brightness of an image. I could apply Curves as a direct adjustment from the image adjustments menu up here, but as you know from other movies, I prefer to use an adjustment layer wherever possible.
And so I'm going to close this menu and go over to the Adjustments panel and I'm going to find the Curves adjustment icon there and click that icon to change the Adjustments panel to the Curves controls and if I look at the Layers panel which I'll do by Double-clicking its tab, you can see that there's now a Curves adjustment layer above the background image layer. I'm going to go back to the Adjustments panel by Double-clicking the Adjustments tab so that I can show you the Curves Interface. The first thing you'll notice is this big graph in the middle of the Curves Adjustments panel.
Inside that graph there is a histogram and this is a histogram that represents the actual tonal values in this image. I have already explained how a histogram works. That it's really a collection of vertical bars each of which represents a different gray scale tone in the image and the height of the bars tells you the relative frequency of a particular tone. You'll notice that this histogram in the Curves Adjustment panel is just like the histogram up here in the Histogram panel. The difference is that as I make my Curves adjustments, the histogram in the Histogram panel will update itself to show me the change and the histogram down here in the Adjustments panel will just stay the way you see it now. So that's why I have the histogram panel open too.
Notice also that there is a horizontal scale at the bottom of this graph and a vertical scale along the left side of the graph. I think I have the horizontal scale as the before scale and the vertical scale as the after scale, because I use the horizontal scale to tell me the gray scale value of a particular point before I make an adjustment and I use the vertical scale to tell me the gray scale value of that same point after I make a Curves adjustment. And the way that I make a Curves adjustment is by changing the shape of this diagonal line, which is the actual curve. The top right of this curve represents the brightest pixels in an image and the bottom left of the curve, the darkest pixels in an image.
One of the simplest ways that I can adjust this curve is to set a black point and a white point in the image if necessary. Now in this case I don't see a reason to set a black point because the histogram is telling me that there already are some pure black pixels in this image. So I'm going to take a look at the white portion of this horizontal scale over here on the right and I can see that there are no vertical bars above the white portion of this scale. So that means that there is no pure white in this image and I can see that if I look at the image even this whitewashed fence looks pretty gray. So what I want to do is to set the white point, and I'm going to do that almost the same that I did in Levels.
I'm going to hold down the Option or Alt key. I'm going to click on this white slider in order to bring up this Threshold view. That will help me to know where to place the white slider and then I'm going to drag to the left. And notice that that control point at the top of the curve is moving to left along with me. When I start to see some small pixels of white in the image I'll release my mouse and I have now reset the white point. I can use the before and after scale to understand exactly how I have changed the brightest tones in this image. This black square up here is the control point that represents the brightest tones.
It used to be over here in the top right corner. If I move directly down from that point to the before scale at the bottom of the Curves graph, I can see the gray tone that used to be the brightest tone in the image. Now if I go back to that black control point and I move directly to the left, I can see on the vertical scale, the current value of the brightest points in the image and that is this pure white that I see here. And if I would like to see that numerically I can look down at the output and input fields here which are telling me that the brightest tone in the image used to be about 200 on a scale of 0- 255. And now the brightest tone is 255.
Another thing to look at in the Curves graph is this diagonal line, which is the baseline curve, and then this line is the current curve. When this line is above the baseline, the image is brighter and when this line is below the base line, the image would be darker. Another thing that I could do with this curve would be to use it to increase the exposure of the entire image. The simple way to do that is to move my mouse over approximately the mid-point of the curve, click there to set an anchor point and then click-and-drag on that anchor point up in order to increase the overall Exposure of the entire image.
Another way to move that point would be to use the arrow keys on my keyboard and I actually prefer to do it that way because the arrow keys make changes in small increments and when you are using Curves often making small changes is the best way to go. So I'm going to press the down arrow on my keyboard, which is reducing the overall Exposure of the image. If I would like to reduce the Exposure in larger increments I'll hold on the shift key as I press the Down arrow key. And to increase Exposure, I'll hold the shift key as I press the Up arrow key. Using the mid-point of a curve to change the overall Exposure of an image is very much like moving the gray input level slider in a Levels adjustment.
But that's not all you can do with Curves. With Curves you can change the exposure of any point on the curve. To show you that I'm going to remove the control point that's currently on the curve and the curve will snap back to where it was just after I moved this white slider. To remove that control point I'll click on the control point, hold on my mouse and then with one movement I'm going to click-and-drag off of the curve and I'll release the mouse. Now let's say that I decide I want to adjust the exposure of all the image except the white door. To do that I'm going to lock down the points of the curve that represent bright pixels in the image. I'll just come in to the curve and I know that this portion of the curve represents the bright areas. So I'm going to click a few times on the curve in the portion that controls the bright parts of the image.
Then I'm going to come down to portion of the curve that controls the darker parts of the image and I'll click there and then I'm going to use the arrow keys on my keyboard to increase Exposure. I'll hold on the Shift key and the Up arrow key and as you can see I'm increasing the exposure of the Adobe without really increasing the exposure of the white door which is locked in place by these three Anchor Points. And if I have gone too far and I want to go back the other way I'll press my Down arrow key and what's moving is just this one selected Anchor Point.
So that's how you can use Curves to adjust the Exposure or Brightness of an image. There's one more thing that I usually do when I make a Curves adjustment and that is to go back into the Layers panel, which I do by Double-clicking the Layers panel tab, selecting the Curves adjustment layer and changing its blend mode from Normal to Luminosity. The reason that I do that is that a Curves adjustment sometimes affects the color in an image and changing the blend mode of a Curves adjustment layer to luminosity eliminates that color change.
So with that introduction to Curves adjustment controls and to the use of Curves to control Exposure you should be getting a sense of the power of this important adjustment. But controlling Exposure isn't the only thing you can do with Curves. Stay with me for the next movie to learn how to control Contrast with a Curves adjustment.
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