Bit-Mapped Graphic Data: Input (Capture) Hardware

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. Scanner • Capture images from a flat object • Linear CCD • Narrow strip passes over image. • Requires 3 images for colour • Red, Green & Blue

5. Bit-Mapped Graphic Data:Storage of Graphic Data Multimedia - Section 2

6. File Formats • Bitmap (BMP) • Graphic Interchange Format (GIF) • Joint Pictures Expert Group (JPEG) • Portable Network Graphics (PNG)

7. Bitmap File Format Uncompressed: • A file which holds a binary number for each pixel in an image Limitation: • large file size Extension: • .bmp

8. Bitmap File Format Colour Depth • The number of colours that can be represented • Calculation: Number of colours = 2 bit depth

9. Example Colour (bit) Depth = 8 Number of colours = 28 = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256

10. GIF File Format • Lossless compression • Limited number of colours: limited to 28 • 256 colours • Features: • Animation • Transparency • Extension: .gif

11. Good For: Flat areas of colour Few colours Animated images Transparency Not Good For: Photographic images High colour graphics High quality videos GIF File Format

12. JPEG File Format • Lossy compression • Greyscale or full-colour image compression • Exploits human eye limitations • Extension: .jpg

13. 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

14. Bit-Mapped Graphic Data:Storage of Graphic Data- Technical Terms Multimedia - Section 2

15. 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

16. 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

17. Dithering Example 4 Colour Non-Dithered 4 Colour with Dithering 256Colour

18. Bit-mapped Graphic Data • Anti alias • Low resolution images can appear less jaggy if extra colours are used to reduce staircase effect

19. 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

20. 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.

21. Bit-Mapped Graphic Data:Output of Graphic Data Multimedia - Section 2

22. 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).

23. Graphics card

24. 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 Hardware for Displaying 2D Graphics