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Mm Unit 2 Part 2
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Mm Unit 2 Part 2






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Mm Unit 2 Part 2 Mm Unit 2 Part 2 Presentation Transcript

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