User Guide

Canvas 12 User Guide
Are you scanning line art or text?: Line art, such as pen and ink drawings, and high-
contrast images with sharp edges or type, should be scanned at the highest resolution
possible. Text scans that will be processed with character-recognition software should also
be scanned at high resolution for accurate translation.
What halftone screen frequency will be used for printing?: For continuous-tone
images (photographs), a common rule of thumb is to scan at a resolution of 1.5 or at most 2
times the screen frequency. For example, for offset printing on newsprint at a screen
frequency of 85 lines per inch (lpi), an image should be scanned at 128 to 170 ppi. For
images printed at 133 lpi, scanning resolution should be 200 to 266 ppi.
Because resizing tends to blur an image, you can use the Unsharp Mask filter to
sharpen it. For more information, see "Sharpen filters" on page 479.
Talk with service bureaus and commercial printers about the screen frequency used for your
projects. With this information, you can let Canvas calculate the optimal resolution for an image
(see "Resampling and sharpening images" on page 458).
Will the final image be smaller or larger than the original?: If you need to enlarge
the image, you should scan it at a higher resolution to retain the most information when you
resize it. If you will reduce the size of the image, you can scan it at a lower resolution.
About digital images and resolution
Digital images, also known as raster and paint images, are composed of tiny square pixels.
The number of pixels that fit in a linear inch or centimeter is the image resolution. The resolution
indicates how much information is in the image, independent of the resolution used to display the
image on screen or to print it.
Low-resolution images have larger pixels and look more jagged than high-resolution images.
However, while high-resolution images look smoother, they also require more memory and disk
space.
Changing image size
You can use several methods to resize or scale paint objects and the images they contain.
Keep in mind that altering the size or resolution of a paint object can degrade the quality of an image.
Canvas uses interpolation to estimate pixel values when necessary, but this can result in loss of
sharpness or detail when large scaling factors are applied.
The best way to avoid image degradation is to avoid changing image size or resolution.
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