2a Bitmapped Graphics Hardware

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2a Bitmapped Graphics Hardware

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

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