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Digital Design for Print and Web: An Introduction to Theory, Principles, and Techniques by John DiMarco, Ph.D.

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CHAPTER 5
Raster Graphics
Chapter Objectives
Identify and define raster graphics.
Identify and define the differences between raster graphics for print and Web.
Introduce basic raster graphics techniques.

Digital Imaging and Raster Graphics

Digital imaging refers to the manipulation of bitmapped images, also known as raster graphics, which are made up of small rectangles called pixels. Pixels, a word that is a shortened version of “picture elements,” are bits of data mapped to a color and arranged in rows and columns within a digital document. The small rectangles form a complete image when viewed together. The size of the rows and columns (i.e., their height and width) represents the page size. The amount of pixels per inch (ppi) in relationship to the page size is used in raster imaging programs to represent resolution output on a screen. The number of dots printed in a linear inch (dpi) is the resolution output on a printer.
FIGURES 5-1, A, B Close-up of image pixels in a raster graphic. Bitmapped images are formed by rectangular squares called pixels.
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The main difference between the final output of print and Web projects is resolution. High resolution—generally 300 to 350 ppi at 100 percent of the image size—is used for all print output, whether to paper or another material, ...

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