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Hardware issues in graphics

Hardware issues in graphics. Istvan Pely (www.movkup.com). It’s a magic act. Computer graphics cheats Two dimensional Discrete frames Light calculations are approximate But it works Cheats are designed for our visual system. Does A = B?. Constructing the world.

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Hardware issues in graphics

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  1. Hardware issues in graphics

  2. Istvan Pely (www.movkup.com)

  3. It’s a magic act • Computer graphics cheats • Two dimensional • Discrete frames • Light calculations are approximate • But it works • Cheats are designed for our visual system

  4. Does A = B?

  5. Constructing the world • We see color, shape and motion that does not really exist - we infer and interpret

  6. The visual system

  7. FAA Human Factors • FAA

  8. Psychophysics • Joy of Visual Perception • Michael Bach • Hoffman • Temporal resolution/stop motion

  9. Bitmap graphics • Image stored as array of numbers • What monitors display

  10. Vector graphics • Picture stored as commands to draw shapes • Takes less storage • Can be resized without pixelation • Used in PowerPoint Disk (50,50,100, red) Square(60,60,200, orange) Line(50,50,100,100)

  11. Vector graphic has to be rendered to display as bitmap on screen Need to convert mathematical shape to pixels on screen Which pixels to turn on? Rasterization Vector to Bitmap

  12. Antialiasing • Smoothing at edges of object • Average colors to avoid the “jaggies” • Average by portion covered

  13. Image Dimension (resolution?) • Dimensions of image • Width by height • Example: 200 by 200 = 4,000 pixels • Example: 20 by 30 = 600 pixels • Example: 1,000 by 2,000 = 2 million • Mega pixel camera • Pixels greater than 1 million

  14. Print resolution • Size of image when printed • Measured in DPI (Dots Per Inch) • Most printers are effective > 100 DPI • A 1000 pixel image would be 10 inches across when printed at 100 DPI

  15. Photoshop Size Dialog Box

  16. Color monitors • Additive color scheme • Red Green Blue • Matches RGB rods in our eyes • Printers - subtractive color scheme CYMK • Cyan, Yellow, Magenta, K for black

  17. Red Channel Green Channel Blue Channel Original RGB Greyscale

  18. Bits/pixel Original at 8 bits (256 levels)

  19. Grey scale resolution

  20. Color resolution • Color depth - number of bits per pixel • Black and white - 1 bits (2 values) • Greyscale - 8 bits (256 values) • True color - 24 bits per pixel • 8 bits each for Red, Green, Blue (RGB) • Indexed color • 8 bit index into 24 bit color table (palette)

  21. Color palette (2-bit example)

  22. Two palettes • Web safe system Full spectrum

  23. Dithering

  24. Image size problem • 400 by 400, true color image • Size in bytes is ? _________________ • 400 * 400 = 16,000 pixels • True color is 24 bits per pixel (3 bytes) • Result: 16,000 * 3 = 48,000 bytes • 48KB using 1000 = K approximation

  25. Size problem 2 • 100 by 100 image • 8 bit Indexed color image • Size in bytes?

  26. Image problem 3 • 1024 by 1024 image • Black and white (bits per pixel?) • How many bytes?

  27. Fourth problem • 500 by 200 image • 10 bits per color (RGB) • Size in bytes?

  28. Basic Graphics Card Video controller Scan controller Video DAC

  29. CRT video trace (scan controller) • Horizontal retrace • Vertical retrace • Blanking periods • Used for double buffering

  30. Graphic acceleration Graphics Processing Unit (GPU) NVIDIA GeForce 7800

  31. Output Primitives • Polylines • Text • Filled regions • Raster images • Incomplete list, but polyline is essential idea

  32. Input primitives • String • Choice • Valuator • Locator • Pick

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