A printer has a spreading unit 1 for spreading data sent from an upper apparatus into bit map data, a memory unit 2 for storing the bit map data spread by the spreading unit 1, an extracting unit 3 for extracting a contour-protecting shaped matrix which prevents the disappearance of a contour of an image, and a printing unit 7 which stores template data and a toner consumption saving pattern and which prints dot data of the bit map data based on a shape of the contour-protecting shaped matrix. The extracted matrix data are compared with the template data. When the matrix data corresponds with the template data, a noted pixel positioned in a central portion of the matrix is replaced with the toner consumption saving pattern. Accordingly, numbers of black dots can be decreased in a part of image data to save toner consumption in the printer.
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