Creating high-contrast ‘posterized’ images You can condense the brightness variations in an image with the Pos- terize command. If you apply the Posterize command to a photo- graph, it creates a high-contrast image by compressing hundreds of brightness levels into only a few. You set the number of brightness levels you want to retain, and Canvas reduces each color channel to that number of values. The Posterize command’s effect depends on the mode of the image you posterize; e.g., if you apply the Posterize command with a setting of 2 levels to a grayscale-mode image, the image becomes black and white. If you apply the same setting to an RGB-mode image (even if it contains only grays), the command converts each pixel’s red, green, and blue value to either zero or full color, reducing the image to eight colors — red, green, blue, red-green, red-blue, blue-green, black, and white. To posterize an image 1 Select one or more paint objects to posterize all the images. You can select an area in one image in edit mode to posterize the selected area only. If you don’t make a selection, the entire image is affected. 2 Choose Image > Adjust > Posterize. 3 Enter a level from 2 to 255. Higher numbers produce subtle effects. Lower numbers produce high-contrast images. 4 After you enter the Levels setting, click OK. Original RGB image Posterize 4 levels Posterize 2 levels Posterize 8 levels Tip You can’t use the Posterize command on images in Black & White or Indexed mode.
Canvas 8 Help: Image adjustment and correction (4 of 24)                                            Page #686