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Mm Unit 2 Part 1
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Mm Unit 2 Part 1

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Transcript

  • 1. Bit-Mapped Graphic Data: Input (Capture) Hardware Multimedia – Section 2
  • 2. CCD & ADC
    • CCD ( charged coupled device ) :
      • Uses sensors to capture light and then convert into analogue electrical signals.
      • Currently only see light levels not colour
    • ADC (Analogue/Digital Converter)
      • Converts the analogue signals into digital signals so that the computer can process them.
  • 3. Digital Camera
    • In a digital camera a CCD array captures light coming in through a lens
    • The Resolution is the number of pixels in the image produced
    • Capturing colour
      • A colour filter array is placed over the CCD array
      • Each sensor records light of one colour (red, green or blue)
  • 4.  
  • 5. Scanner
    • Requires 3 images for colour
      • Red, Green & Blue
    • Capture images from a flat object
    • Linear CCD
      • Narrow strip passes over image.
  • 6. Bit-Mapped Graphic Data: Storage of Graphic Data Multimedia - Section 2
  • 7. File Formats
    • Bitmap (BMP)
    • Graphic Interchange Format (GIFF)
    • Joint Pictures Expert Group (JPEG)
    • Portable Network Graphics (PNG)
  • 8. Bitmap File Format
    • Uncompressed :
      • A file which holds a binary number for each pixel in an image
    • Limitation :
      • large file size
    • Compression :
      • RLE (Run Length Encoding)
        • uses the fact that large areas have same colour of pixel. ( LossLess )
    • Extension:
      • .bmp
  • 9. Bitmap File Format
    • Colour Depth
    • The number of colours that can be represented
    • Calculation:
        • Number of colours = 2 bit depth
  • 10. Example
    • Colour (bit) Depth = 8
    • Number of colours = 2 8
    • = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2
      • = 256
  • 11. GIF File Format
    • Lossless compression
      • LZW
    • Limited number of colours: limited to 2 8
      • 256 colours
    • Features:
      • Animation
      • Transparency
    • Extension: .gif
  • 12. GIF File Format
    • Good For:
    • Flat areas of colour
    • Few colours
    • Animated images
    • Transparency
    • Bad For:
    • Photographic images
    • High colour graphics
    • High quality videos
  • 13. Interlacing
    • Allows you to view an image before it is downloaded
    • Image is gradually revealed
  • 14. JPEG File Format
    • Lossy compression
      • DCT
    • Greyscale or full-colour image compression
    • Exploits human eye limitations
    • Related to MPEG
    • Extension: .jpg
  • 15. JPEG File Format
    • Advantages:
      • Greater compression than lossless
      • Good for photographic images (real-world)
      • Compression ratio can be controlled by user
      • Best for large files
    • Disadvantages
      • Doesn’t support interlacing or transparency
  • 16. PNG File Format
    • Has all advantages of GIF without the restrictions
    • Allows 24 bit colour
    • Allows for partial transparency
    • Lossless compression
      • Variation of LZW
    • Extension: .png

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