User Guide

Chapter 5: Painting And Image Editing
If you select an area within an image, Canvas applies the adjustment only to that area. Otherwise,
Canvas adjusts the selected paint objects.
Setting a brightness threshold
Use the Threshold command to convert any image to black and white. The Threshold command
compares each pixel’s brightness value to a threshold value that you set. It changes brighter pixels
to white and darker pixels to black. The threshold setting is based on a scale of brightness values
from 0 (black) to 255 (white). You can’t use the Threshold command on images in Black & White or
Indexed mode.
For example, if you set a threshold value of 128, pixels that are brighter than medium gray become
white, while pixels darker than medium gray become black.
To map an image to black and white:
1. Select one or more paint objects to adjust all the images. You can select an area in one image
in edit mode to adjust the selected area only. If you don’t make a selection, the entire image
is affected.
2. Choose Image | Adjust | Threshold.
3. Enter the threshold value by dragging the slider or typing a number in the text box. If you
want Canvas to convert half the pixels to black and half to white, click Auto.
4. Click OK after entering the setting you want.
To isolate selections, apply the Threshold command in conjunction with the High Pass filter to an
image in an alpha channel (see "Isolating areas using the High Pass filter" on page 538).
Creating high contrast posterized images
You can condense the brightness variations in an image with the Posterize command. If you apply the
Posterize command to a photograph, 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.
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