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Mm Unit 2 Part 2


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Mm Unit 2 Part 2

  1. 1. Bit-Mapped Graphic Data: Storage of Graphic Data - Technical Terms Multimedia - Section 2
  2. 2. Bit-mapped Graphic Data <ul><li>To calculate the approx file size of an uncompressed bitmap: </li></ul><ul><li>Files size (bytes) = </li></ul><ul><li>Number of Pixels x colour depth per pixel (bits) </li></ul><ul><li>8 </li></ul><ul><li>If colour depth per pixel is in bytes : </li></ul><ul><li>Files size = Number of Pixels x colour depth per pixel </li></ul>
  3. 3. Bit-mapped Graphic Data <ul><li>Dithering </li></ul><ul><ul><li>Extra colour can be created by placing different colours next to each other </li></ul></ul><ul><ul><li>Red and blue pixels would appear as purple </li></ul></ul>
  4. 4. Dithering Example 256 Colour 4 Colour Non-Dithered 4 Colour with Dithering
  5. 5. Bit-mapped Graphic Data <ul><li>Anti alias </li></ul><ul><ul><li>Low resolution images can appear less jaggy if extra colours are used to reduce staircase effect </li></ul></ul>
  6. 6. Bit-mapped Graphic Data <ul><li>Re-sampling </li></ul><ul><ul><li>If detail is lost in a graphic it is not possible to retrieve it </li></ul></ul><ul><ul><li>Re-sampling will make a best guess at what the missing pixels would look like </li></ul></ul><ul><ul><li>Technique used to enhance grainy security camera images </li></ul></ul>
  7. 7. Trading quality for file size <ul><li>Resolution: increasing resolution increases the number of pixels, can improve the quality of a graphic but increases the file size. </li></ul><ul><li>Colour depth : increasing colour depth increases the number of colours or shades of grey, can improve the quality of a graphic but increases the file size. </li></ul><ul><li>Lossy compression: reduces file size and, providing the rate of compression is not too high, does not affect the quality of the graphic. </li></ul>
  8. 8. Bit-Mapped Graphic Data: Output of Graphic Data Multimedia - Section 2
  9. 9. Graphics cards <ul><li>The graphics card is the device in the computer responsible for generating images. </li></ul><ul><li>Images are held in the memory of the graphics card (called VRAM - or Video RAM). </li></ul>
  10. 10. Digital to Analogue Converter (DAC) <ul><li>Converts the digital computer signal into an analogue one that the monitor needs. </li></ul><ul><li>In future analogue displays will be replaced with ones that accept digital signals </li></ul><ul><li>Many LCD displays currently allow digital signals </li></ul><ul><ul><li>Called DVI - Digital Visual Interface </li></ul></ul>Digital Image Signal DAC on Graphics Card Analogue Image Signal
  11. 11. Graphics Processing Unit (GPU) <ul><li>The GPU is a Digital Signal Processor (DSP) </li></ul><ul><li>Located on the graphics card </li></ul><ul><li>Often more advanced than CPU </li></ul><ul><li>Created mainly for modern gaming </li></ul><ul><li>Generates images faster and with better quality than if generated from the processor </li></ul>
  12. 12. Hardware for Displaying 2D Graphics <ul><li>CRT monitor: </li></ul><ul><ul><li>Bulky & heavy </li></ul></ul><ul><ul><li>Run on mains power </li></ul></ul><ul><ul><li>Cost less than equivalent TFT screens </li></ul></ul><ul><li>LCD and TFT screens: </li></ul><ul><ul><li>Flat & light </li></ul></ul><ul><ul><li>Need less power </li></ul></ul><ul><ul><li>More expensive than CRT </li></ul></ul>