1. Summer Term Year 10 Slides

2. Data Representation: Bitmap Images Week 1 Lesson 1

3. Bitmap images

4. Bitmap images

5. Data Representation: Bitmap Images Week 2 Lesson 1

6. Bitmaps
a bitmap is a type of memory organisation or image file format used to store digital images

7. Displays text and graphics on a VDU/monitor
Bit-mapped Images
Displays text and graphics on a VDU/monitor
screen divided up into a grid
each square on the grid is a Pixel
How?
Bits controlling a pixel stored in a specific memory location
Consecutive memory locations hold all the codes controlling the screen
Computer scans the memory and generates the picture by lighting screen pixels with the colour code for the individual pixel

8. Colour and bit maps
Each pixel is individually coloured
Number of colour bits used (colour depth) determine the number of colours available
Pixels are stored with a colour depth of 1, 4, 8, 16, 24, 32 bits per pixel
1 bit black or white (1 or 0)
24 bit: 224 colours with 8 for each of red, green and blue
32 bit: used for simplicity with 32 bit computers – additional 8 bits not normally used for colour

9. File size 1 byte is used per pixel to store the location
Additional bytes used for colour depth
E.g x 768 screen requires bytes for image
X 3 (if 24 bi colour (3 bytes x8bits =24 bits))
So: 1024 x 768 x 3 = bytes

10. Pixels per inch
The more pixels there are, the sharper and clearer the image will be (but remember the more pixels there are, the bigger the file size too)
Bitmap images

11. Units of measurement 4 bits = 1 nibble 8 bits = 1 byte
1024 bytes = 1 kilobyte (KB)
1024 KB = 1 megabyte (MB)
1024 MB = 1 gigabyte (GB)
1024 GB = 1 terabyte (TB)
Bitmap images

12. Data Representation: Sound Week 3 Lesson 1

13. Analogue sound wave
Bitmap images

14. Sampling rate
Sampling rate is the number of samples taken per second from an analogue sound wave
Too few and the resulting digital sound will not sound like the recording
Too many and the file size will be very large
Bitmap images

15. Sampling resolution
Sampling resolution is the number of bits that are assigned to each sample taken
Too few and there will be less sound levels
Too many and the file size will be very large
Bitmap images

16. Analogue sound wave: varies continuously

17. Digital sound wave: discrete
amplitude’ of curve sampled at regular intervals
accuracy determined by number of bits used (resolution)

18. Basic set of measurements

19. Increase the sampling rate

20. … now increase the resolution

21. The impact:
Bitmap images

22. Factors to consider in sound recording
Space available for file storage
Sampling rate – more samples mean more data but better quality
Resolution – higher resolution mean more data but better quality
Bandwidth for transmission e.g. over internet
Common formats: WAV MPEG etc.