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Mm Unit 2 Part 1
 

Mm Unit 2 Part 1

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    Mm Unit 2 Part 1 Mm Unit 2 Part 1 Presentation Transcript

    • Bit-Mapped Graphic Data: Input (Capture) Hardware Multimedia – Section 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.
    • 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)
    •  
    • Scanner
      • Requires 3 images for colour
        • Red, Green & Blue
      • Capture images from a flat object
      • Linear CCD
        • Narrow strip passes over image.
    • Bit-Mapped Graphic Data: Storage of Graphic Data Multimedia - Section 2
    • File Formats
      • Bitmap (BMP)
      • Graphic Interchange Format (GIFF)
      • Joint Pictures Expert Group (JPEG)
      • Portable Network Graphics (PNG)
    • 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
    • Bitmap File Format
      • Colour Depth
      • The number of colours that can be represented
      • Calculation:
          • Number of colours = 2 bit depth
    • 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
    • GIF File Format
      • Lossless compression
        • LZW
      • Limited number of colours: limited to 2 8
        • 256 colours
      • Features:
        • Animation
        • Transparency
      • Extension: .gif
    • GIF File Format
      • Good For:
      • Flat areas of colour
      • Few colours
      • Animated images
      • Transparency
      • Bad For:
      • Photographic images
      • High colour graphics
      • High quality videos
    • Interlacing
      • Allows you to view an image before it is downloaded
      • Image is gradually revealed
    • JPEG File Format
      • Lossy compression
        • DCT
      • Greyscale or full-colour image compression
      • Exploits human eye limitations
      • Related to MPEG
      • Extension: .jpg
    • 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
    • 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