The Curves feature is similar to Levels. Both features let you adjust the tonal range of an image. Whereas Levels uses the highlights, shadows, and midtones to correct the tonal range, Curves lets you adjust any color along the tonal range (from the darkest pixels to the lightest pixels) without affecting other colors.
The grid in the Curves dialog box depicts these brightness values:
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The horizontal axis depicts the original brightness of the pixels (shown in the Input box). |
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The vertical axis represents the new brightness values (shown in the Output box). |
When you first open the Curves dialog box, the diagonal line indicates that no changes have been made, so the input and output values are the same for all pixels.
To adjust a specific point in the tonal range:
| 1 | Select the image in either object mode or image edit mode. |
| 2 | Choose Xtras > Adjust Color > Curves. The Curves dialog box opens.
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| 3 | Choose Preview to view your changes in the workspace. As you make changes, the image updates automatically. |
| 4 | From the Channel pop-up menu, choose whether you want to apply changes to individual colors or to all color channels. |
| 5 | Click a point on the grid's diagonal line, and drag it to a new position to adjust the curve. |
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The horizontal axis corresponds to the Input value (the original brightness of the pixels). The vertical axis corresponds to the Output value (the adjusted brightness of the pixels). |
| Each point on the curve has its own Input and Output values. When you drag a point, the Input and Output values update automatically. | |
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The diagonal line displays brightness values of 0 to 255, with 0 representing the shadows.
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| Diagonal line after dragging a point to adjust the curve. |
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For information on using the dropper buttons to adjust the tonal range, see Adjusting the tonal range with the eyedroppers.
Note: Clicking the Auto button yields the same result as clicking the Auto button in the Levels dialog box.
To delete a point along the curve:
Drag the point off the grid.
Note: You cannot delete the endpoints of the curve.