Unit 2 - Data Representation

• Bit - a single 0 or 1

  Byte - 8 bits

  A nibble - 4 bits
• The most significant bit is the bit with the largest value (furthest left)

  The least significant bit is the bit with the smallest value (furthest right)

  e.g: 11001 -> 1+8+16

  msb = 16

  lsb = 1
• Advantages to hexadecimal:

  • simpler to remember than a binary value
  • Less likely error
  • Easier to write than binary
  • Easy to convert between hex and binary
• Hex to binary conversion:

  3B

  3 = 0011

  B = 1011

  so 3B = 00111011
• A pixel is the smallest identifiable area of an image
• PPI stands for pixels per inch

  DPI stands for dots per inch (for printers)
• file size (unit - bits)= sample rate (unit - samples per second) * bit depth * duration
• Calculating file size

  Bits - 4 as the scale is from 0 to 15

  Samples per second - 6

  Duration - 3 seconds

  file size = 6 * 4 * 3

  = 72 bits

  = 9 bytes

  
• An overflow error when adding binary values is when the result of the addition has more bits than the computer can handle
• ASCII stands for American Standard Code (for) Information Interchange
• Unicode is an international character encoding standard that provides a unique number for every character across languages and scripts, making almost all characters accessible across platforms, programs, and devices.
• The amount of colours than can be represented by an image is 2 to the power of its number of bits

  e.g: image with 8 bits:

  2 ^ 8 = 256
• Lossy compression removes sounds that we can’t easily hear or that least affect the perceived playback quality
• Metadata is information other than image data that is stored with the file of the image. It includes:

  • Colour depth
  • Resolution
  • Date created
  • Author
• Outline what happens when a computer converts music into a file

  • Analogue sound is converted from sound waves into binary
  • By taking samples at regular intervals
  • Which measure the amplitude each sample
• Show the effect of a binary shift right of two places on the binary number 00110100?

  • 00110100 = 4 + 16 + 32 = 52
  • 00001101 = 1 + 4 + 8 = 13
  • The number is halved twice
• A bitmap is a file format used to store digital images. Bitmap images are organised as a grid of coloured squares called pixels. Each different colour in the image is stored as a binary number.

  When zooming in or enlarging a bitmap image, the pixels are stretched and made into larger blocks. The quality of bitmap images reduces as they are enlarged.
• Image quality is the detail of an image determined by the colour depth and resolution
• The maximum amount of colours an image can represent is 2 to the power of the colour depth in bits.

  e.g: an image with a colour depth of 4 can display 16 colours
• Each sample of the amplitude recorded when converting sound to digital is stored as a binary number
• Bitmap image has 3 colours and is 15 by 6 pixels. The fewest number of bits to store it is:

  Resolution - 15 * 6 = 90

  Colour depth of 2 -> 1 bit = 2 colours, 2 bits = 4 colours

  90 * 2 = 180 bits
• The bit depth of a digital sound means the number of bits used to store each sample
• The binary number for each sample is stored sequentially when converting from analogue to digital sound
• A Character set is all the different characters a computer can repeesent
• File size in a text file = bits per character * number of characters