Halftones

Commercial printing presses cannot produce true shading but can create the illusion of shading, by printing images made up of tiny dots. In conventional screening, the size of the dots determines the different levels of shading (that is, the bigger the dots, the darker the shade). In Stochastic screening, the frequency of the dots determines the different levels of shading (the more dots in an area, the darker the shade). A halftone screen is necessary to convert images with true shading to images made up of tiny dots.

Originally, a halftone screen was an opaque screen with thousands of tiny holes. An image with shading was photographed through this screen using special photographic paper or film. The resulting image consisted entirely of dots. This image was then used to create printing plates.

Now, however, you can create halftone images without using screens or cameras. To ensure that the bitmaps print correctly, you must set the halftone screen frequency and bitmap resolution correctly.

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