Summer Term Year 10 Slides

Data Representation: Bitmap Images Week 1 Lesson 1

Bitmap images

Bitmap images

Data Representation: Bitmap Images Week 2 Lesson 1

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

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

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

File size 1 byte is used per pixel to store the location Additional bytes used for colour depth E.g. 1024 x 768 screen requires 768 432 bytes for image X 3 (if 24 bi colour (3 bytes x8bits =24 bits)) So: 1024 x 768 x 3 = 2 359 296 bytes

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

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

Data Representation: Sound Week 3 Lesson 1

Analogue sound wave http://www.minelab.com/usa/knowledge-base/getting-started/glossary-of-terms Bitmap images

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

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

Analogue sound wave: varies continuously

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

Basic set of measurements

Increase the sampling rate

… now increase the resolution

The impact: http://www.music.columbia.edu/cmc/musicandcomputers/chapter2/02_05.php Bitmap images

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.