You can adjust the tonal range of an image with the Curves command. Unlike the Levels command, which can set the minimum, maximum, and median values, Curves adjusts the entire range of values. It lets you map input values to output values according to a line (“curve”) on a graph. Curves provides the most control over the tonal range of an image.
This command is not available when a paint object in Black & White mode or Indexed mode is selected.
In the Curves dialog box, brightness values range from 0 (black) to 255 (white), or 0 percent (white) to 100 percent (black). To switch between these scales, click the grayscale bar under the graph.
A typical setting is a gentle S-curve (or inverted S-curve, depending on the scale you use), which adds contrast to an image without appearing too harsh.
The graph shows how Canvas X Draw maps input brightness values to output values. Select Preview to see the effect on the image.
Choose a channel to adjust.
The grayscale ramp shows the lightness scale, either 0-255 (dark to light) or 0-100 percent (light to dark). Click the ramp to reverse the scale and the curve.
Input and Output
Type brightness values in the Input and Output boxes. Or, drag the pointer (circled) to specify brightness values.
Click this icon and drag a point on the curve to reshape the curve. Click the curve to add up to 19 control points. Drag points off the curve to delete them.
To draw a disconnected segment, click this icon and drag in the graph.
With the pencil selected, click to smooth the curve.
To redraw the curve completely, or to create sharp changes in brightness for a tonal range, click the pencil and draw a new curve or segment.
You can save Curves dialog box settings to use again; e.g., after correcting the brightness curve for a particular Photo CD image, you can save these settings and later apply them to other images from the same source.
In the Curves dialog box, click Save. In the directory dialog box, type a name for the settings file, select a location, and click Save.
In the Curves dialog box, click Load. In the directory dialog box, locate the settings file and click Open.