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Mm Unit 2 Part 2

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