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If you were on a desert island with your computer and Photoshop and some kind of solar energy, and you could only have one tonal and color correction feature with you, what feature would that be? I'd say Curves. Curves is the most complete of the tonal and color correction features in Photoshop. In this movie, I'd like to show you how to use Curves to adjust contrast and brightness in an image. It's very much like making the same kinds of adjustments with Levels, as I showed you how to do in another movie. But with Levels, you could only adjust the tonality of three points: a shadow point, a highlight point, and midtones.
By contrast with Curves, you have the flexibility to adjust any of the 256 grayscales tones in an image. So once you're comfortable learning Levels, I suggest that you give Curves a try too, when you're making changes to brightness and contrast. Curves are also used for color correction, but that's not going to be the focus of this lesson. In this lesson, we would be looking just at adjusting brightness and contrast of tones. Like all the adjustments in Photoshop, when I apply a Curves adjustment, I try to use an adjustment layer rather than a direct adjustment.
To apply a Curves adjustment layer, I'll go to the Adjustments panel here, and I'll click the third icon from the left in the top row. That adds this Curves adjustment layer in the Layers panel and it changes the controls in the Adjustments panel to the Curves controls. Let's take a quick look at what's here. In this box, there is a baseline curve, which represents at the top right the brightest possible tones, and in the bottom right, the darkest possible tones with all the great tones in between.
It's similar to the Bar Chart in the Levels dialog box but turned up on its end 45 degrees. You can see a Histogram in the Curves dialog box that represents the initial tones in the open image. You can use this as a reference, but I also suggest that you have your Histogram panel open, so you can see the Histogram update as you make changes in the Curves Adjustments panel. There are two gradients here in the Curves Adjustments panel. The one on the bottom represents the current tones in the image, with dark tones on the left and light tones on the right.
When you use Curves, you are remapping those tones to other tones and those are represented in the vertical bar here with dark on the bottom and right on the top. So for example, if I click in the middle of this curve and then I drag up, notice the horizontal line that's intersecting the vertical bar on the left. What it's telling me is that the middle gray that I've currently got under my cursor is being changed to a lighter gray as I move up the vertical bar chart. I press Reset to eliminate that curve.
And now let me quickly show you some of the Preset Curves that come with the Curves Adjustments panel. Those are located here at the top of the panel, in this menu. I want you to see what happens when you make a curve to darken an image. As you can see this kind of a curve bows down beneath this light gray baseline reference. And if I go up to the Presets and I choose Lighter, I get the opposite, a curve that bows up above the baseline reference line.
And if I go back to the Presets and choose Increase Contrast, I get an S-shaped curve, which goes up in the highlight area and moves below the baseline reference point in the shadow area. This kind of a curve is typically used to increase contrast. I'll press Reset again. And let's go ahead and make a curve to improve the contrast and brightness in this image. The first step is to go to the sliders at the bottom of the Curves panel. This white slighter right over here on the right is just like the white slider in the Levels dialog box.
Before I move that slider, I am going to go to the panel menu, up here at the top of the Adjustments panel and make sure that Show Clipping for Black/White Points is checked. That way I don't have to hold down the Option key on the Mac or the Alt key on a PC in order to see where to place this slider. So as I drag to the left to set the white point for the image, I go until I see some colored and white pixels. Those pixels are going to be pushed to pure white as well everything to the right of the place that I leave this slider.
I'll do the same on the left with the black slider dragging it to the right and right away I do see some pixels at the bottom of the screen, which are already black. So I am going to release my mouse there. Now if I go to the Preview button at the bottom of the Adjustments panel and I press-and-hold, I can see how the image was without this curve, and how it is with this curve. And all I have done so far is set the black-and-white points. Now what if I also want to lighten the entire image? I could come in and set a point on this curve by clicking right in the middle, and then drag up, but in Photoshop CS4 there is a better way of customizing your curves and that is to use the On Image control which is located right here.
I'm going to click to select that control and then I am going to come in my image and make some visual adjustments. So for example, let's say I want to go to this gray area over here and open it up, so I can see more detail there. You will notice when I move my mouse over that area, a small hollow circle appears on the curved baseline showing me which part of the curve represents these particular colors and then I'll click and I'm going to drag up, and as I do, I am lightning this area of the image and the curve is moving up.
That also sets a point on the curve. So I can go back to that point if I want. Now I am going to move my cursor down here to a darker area and you can see that that's in a lower part of the curve, and I'll click-and-drag down to make that area darker. What I'm doing now is darkening the shadows and creating an S-curve in the Curves Adjustments panel. And as you saw with the Preset an S-curve increases contrast. That's particularly true in areas like this where there is a steep part to the curve.
To recap, I just drag the sliders in to set the white point and the black point, then I click the On Image icon and came into my photograph and clicked and dragged in areas where I wanted to open up highlights or make shadows darker, or you could do the opposite if you wanted to. I am going to preview the image now with this Contrast Curve by pressing down on the Preview icon to see how the image looked without the Curves adjustment layer, and how much more it pops now. You can see that not only the contrast and the brightness changed here but also the color.
This life preserver is really orange now. When you make curves adjustments you often do end up impacting color. And if all you want to do is affect the contrast and the brightness, then you can change the blending mode of the Curves adjustment layer. To do that, I'll go to the Layers panel, make sure that adjustment layer is selected, and go to the Blending Modes menu where I'll click and drag down all the way to the bottom and choose Luminosity. Now let's preview what we have. Here is the image now without that big color change, and here's how it was when I started.
Much more contrasty now. As you have seen Curves gives you a lot of control over the brightness and contrast of particular areas in a photo, and the new On Image control paired with the black and white sliders for setting the black and white points make curves in Photoshop CS4 accessible to everyone.
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