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Dale & Lewis Chapter 3 Data Representation
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Representing color Similarly to how color is perceived in the human eye, color information is encoded in combinations of intensities of red, green and blue colors. Monitors Printers Scanners…
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Color depth Similar to an audio channel, each color channel can be represented by n bits more bits, more levels If each channel uses 8 bits (256 levels), then a color uses 24 bits TrueColor (16+ million colors) More than the human eye can distinguish or hardware reproduce
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Images Now that there is a way to represent color, an image can be constructed with an array of picture elements (pixels) Pixel resolution (how many pixels or dots per inch - dpi) and color depth determine the quality of an uncompressed image
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Image file formats and compression BMP – popular bitmap, lossless but can use run-length encoding to reduce file size GIF (Graphics Interchange Format) – can include an index of colors to reduce file size (i.e. if fewer than 16M+ colors are needed, reduce bits needed for each channel index converts reduced bit encoding to RGB) −A version of GIF defines different frames that can be played back as animation JPEG (Joint Picture Experts Group) – lossy perceptual compression to exploit the eye’s sensitivity to gradual color changes average color hues over short distances PNG (Portable Network Graphics) – a GIF replacement with broader color depth
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Graphics Line art and graphics may contain a lot of empty space and bitmaps are not optimal representations Vector graphics store images as collection of colored lines and shapes −Collection of commands −Complexity determines file size −Resizing can be done with perfect rendering and without loss of information SVG file format (Scalable Vector Graphic)
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Video Timed frame sequence (24 or 30 fps) very large files Complex information difficult compression Codec (COder/DECoder) define how to interpret bits Can be processor-intensive processes some codecs require specialized hardware Temporal compression −Keyframe + delta frames Spatial compression −Groups similar areas of a frame into a large pixel, or compresses frames just as in image files
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Dale & Lewis Chapter 4 Gates and Circuits
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Computers & Electricity Voltage: measure of electrical potential difference −Analogy: water pressure in a garden hose Voltage is variable: for binary representation we only look at off states (low or no voltage) and on states (high voltage, i.e. 5V) Thresholds used to deal with noise: off states (0 2V), on states (2V 5V) Maximum voltage set to prevent damage and for power/speed considerations
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Gates Device that performs a basic operation on electrical signals One or more input signals produces one output signal Basic operations: NOT, AND, OR Other convenient operations: XOR, NAND, NOR Circuits −Combination of interacting gates designed to accomplish a specific logic function −E.g. perform arithmetic, store values
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Notations to describe behavior of gates and circuits Boolean algebra −Variables can take only values of 0 and 1 −Powerful way to demonstrate the activity of circuits Logic diagrams −Graphical representation of a circuit −Each gate is represented by a specific symbol Truth tables −Describes the function of a gate or circuit −Lists all possible input/output combinations
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Gates Six main gate types Can build anything we need from them −Boolean algebra operations: AND, OR, NOT −Convenient: XOR, NAND, NOR −Easier to physically build a NAND gate than AND gate See Chapter 4 slides from the Book…
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