2 a flatbed or rectangular coordinate digitizer is

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Unformatted text preview: owadays CAD packages are extensively used in designing models for aircraft, ship, and building structures, layout of printed circuit boards, and chemical plant pipelines, etc. Based on these drawings, manufacturing information such as parts list, subassembly list, etc., are automatically generated and used by CAM packages. The greatest advantage of using CAD and CAM packages for such applications is that design ideas may be quickly checked and graphically conceptualized interactively, and design changes may be quickly modified, immediately creating accurate assembly drawings and associated parts and subassembly lists. 2. Images. These are pictures and photographs composed of a collection of pixels (short form of "picture element," which is a unit of measurement across a computer screen). As shown in Figure 19.2, the pixels of an image are arranged as a two-dimensional matrix. This two-dimensional (or spatial) representation is called the image resolution. Since the storage representation of images is a direct translation of the image, pixel by pixel, no concept of a line, arc, or circle exists. As shown in the figure, each pixel consists of three components: the red (R), the green (G), and the blue (B). On a display screen, each component of a pixel corresponds to a phosphor. A phosphor glows when excited by an electron gun. Various combinations of different RGB intensities produce different colors. The number of bits used to represent a pixel is called the color depth, which decides the actual number of colors available to represent a pixel. Color depth in turn is determined by the size of the video buffer in the display circuitry. For example, a screen with a 640-by-480 resolution and with 24-b color (i.e., 8 bits each for the R, G, and B components) displays 640 pixels horizontally and 480 vertically, and each pixel can be represented by selecting from more than 2 24 (^ 16.7 million) different colors. The resolution and color depth determine the presentation quality and the size of image storage. The more pixels and the more colors, the better the quality and the larger the volume. For example, a 640-by-480 image with 24-b color requires 640 x 480 x 24b = 7.4 Mb of storage. To red...
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This document was uploaded on 04/07/2014.

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