Adjusting brightness curves You can adjust the tonal range of an image with the Curves com- mand. Unlike the Levels command, which can set the minimum, maximum, and median values, Curves adjusts the entire range of val- ues. 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. Levels dialog box You can use the Levels dialog box to control different aspects of brightness levels. A Choose an individual color channel or the composite chan- nel. B Type values in the Input Levels boxes or drag the slider under the histogram to set the minimum input level, midtone ratio, and maximum input level. C    Enter numbers in the text boxes or drag the sliders to set the minimum and maximum output levels. D    The histogram graphs brightness levels for the select- ed channel. E Click Auto for Canvas to map the darkest values in the selection to black and the light- est value to white. E D B A B C
Canvas 8 Help: Image adjustment and correction (9 of 24)                                            Page #691