Unit 2 - Data Representation

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    • 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