This chapter is from the book
This chapter is from the book
This chapter is from the book
Adjusting contrast and color using Curves
In Photoshop, most image corrections can be done using options in the Adjustments panel. You’ll use a Curves adjustment to improve contrast.
If the Adjustments panel isn’t visible, click its tab to bring it forward or choose Window > Adjustments.
In the Single Adjustments section, click Curves. A new Curves 1 adjustment layer appears in the Layers panel. The Properties panel comes forward and changes to show Curves options, because Curves is the currently selected layer.
A. Curves presets
B. On-Image Adjustment tool
C. Black point eyedropper (color sampler)
D. Gray point eyedropper
E. White point eyedropper
F. Point mode (edit curve by adjusting points)
G. Draw mode (edit curve by drawing freehand)
H. Smooth curve (available when Draw mode is active)
I. Calculate a More Accurate Histogram
J. Composite or single channel curve display
K. Auto button
L. Selected curve point (appears solid)
M. Tone curve
N. Points on the curve
O. Histogram
P. Black point (left) and white point (right); tones outside these sliders are clipped
Q. Input (original) and Output (edited) values of the selected curve point
TIP
The histogram that initially appears is an approximation so that it draws quickly. For full accuracy, click the Calculate a More Accurate Histogram icon (
), the bottom icon to the left of the curve graph.
The Curves graph shows the current tone curve as a straight diagonal line because no curve edits have been made yet. Behind the curve grid you see a histogram, a graph that shows you how much each tonal level in the image is used. To understand the histogram and tone curve, refer to the gradient bars along the left and bottom of the graph. For example, the bottom bar’s gradient shows that black is at the left edge and white is at the right edge. Below it, a dark triangle and light triangle mark the image levels currently used as the darkest and lightest tones, respectively. One way to increase contrast is to drag the triangles inward to exclude extreme levels that aren’t needed for image quality.
The histogram shows that there are image pixels using most tonal levels except those closest to white, so the lightest tone in the image is not near pure white. That helps explain why the image doesn’t have the sunny contrast that it should.
You can shape the curve by adding points, controlling contrast from the darkest to lightest tonal levels. Where the curve steepens, the tones along that segment have more contrast. Where the curve flattens, the tones have less contrast.
In the Properties panel, click the Auto button.
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Photoshop analyzes the image and applies a custom curve with four points. The images brightens because the white point triangle was pulled in to set the lightest tone in the image to white, and also because the curve is high at the light end.
Auto works well for many images, but this image now seems a bit too light and the colors are too cool (blue), so now you’ll try a more precise manual method: The color samplers for a Curves adjustment layer. There are three of them, for the black point, gray point, and white point. You don’t always have to use all of them.
With the Curves adjustment layer still selected, in the Properties panel click the white point eyedropper icon to select it, and click that sampler on the lightest part of the clouds because it’s the lightest tone that should be neutral.
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Notice that the curve changed in two ways: You now see red, green, and blue (RGB) curves because the white end of each of the image’s channels was shifted by different amounts to make the clicked level a neutral white, removing a color cast. Those ends were also brought in slightly to set the brightness of that image level to white, enhancing contrast. Also, this replaces the curve that Auto applied.
In the Properties panel click the gray point eyedropper icon to select it, and click that sampler on something in the image that should be neutral gray. We clicked the large antenna dish in the middle of the image.
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The midtone image colors are rebalanced based on the neutral gray reference you clicked, removing the cool color cast. In the Curves graph the RGB curves update.
You’ve improved both the tonal contrast and the color balance of the image just by refining the end points of the curves. Now refine contrast by shaping the curve.
You can edit the curve by clicking it to add points and then dragging the points to shape the curve. But if you’re still learning, you might not know where on the curve to add points. It’s easier to use the On-Image Adjustment tool to shape the curve by dragging the tool on image tones that you want to lighten or darken.
In the Properties panel, click the On-Image Adjustment tool (
) to select it.
A good way to use this tool is to identify two tonal levels in the image that you want to move further apart (to increase contrast) or closer together (to decrease contrast). In this image the stone buildings could use more “snap,” so focus on those.
Position the On-Image Adjustment tool over the dark roof tiles, then drag down slightly until you think the tiles should be no darker, and then release the mouse button. Notice that a point was added to the curve at the tonal level where you started dragging, and that point pulled down the curve.
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Position the On-Image Adjustment tool over some lighter building walls (we used a wall to the left of the dome), drag up slightly until you think those walls are light enough, and then release the mouse button. Notice that a point was added to the curve at that tonal level, and it now pulls up the curve there.
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The S-shaped curve you created is the typical shape of a curve that enhances midtone contrast, because it’s steeper in the midtones. If you want to adjust it further, drag the points on the curve or click the curve to add more points to drag until you think the image contrast looks right. It’s easier to control a curve with fewer points.
Choose File > Save. Click OK if the Photoshop Format Options dialog box appears; it appears because the document now has multiple layers.
