Representing images, sound and other data exam tips

Exam tips

• Link bits to interpretation

  When explaining how graphics or sound are represented, state both that the data is encoded as bits and that an agreed representation is needed to interpret those bits.

  This directly addresses the key relationship between bit patterns and the forms of data they represent.

• Use the key contrast

  Remember the pair: analogue means continuous, while digital means separate or discrete.

  This directly addresses the defining difference required when comparing analogue and digital data or signals.

• State both the direction and the purpose

  When describing a converter, identify what type of signal enters it, what type leaves it, and why the conversion is needed.

  This directly addresses the principles of operation and helps avoid answers that only give an abbreviation without explaining how the device is used.

• Write the bitmap storage formula first

  Start calculations with size in pixels = width × height, then use storage requirement = size in pixels × colour depth.

  Writing both stages reduces the chance of forgetting one dimension or multiplying by the colour depth incorrectly.

• Link every shape to properties

  When describing a vector graphic, name the objects and then give relevant properties for each one.

  This demonstrates both parts of the specification: the image is a list of objects and each object's properties are stored.

• Link advantages to uses

  When explaining which approach to choose, connect a property of the approach to the purpose of the image.

  For example, link resizeability and sharp shapes to a logo, and pixel-based detail to a photograph. This makes the comparison justified rather than a list of isolated facts.

• Write the calculation in stages

  Calculate the total number of samples first, then calculate the number of bits, and finally convert to bytes.

  Showing each stage makes the units clear and helps prevent errors when using the sound sample size formula.

• Link advantages to representation

  When describing an advantage of MIDI, explain how storing event messages rather than a complete recording causes that advantage.

  An explanation such as 'smaller file size because only musical instructions are stored' is more precise than simply stating 'MIDI files are small'.

• Link the method to the result

  When explaining a compression technique, describe what repeated information is identified, how it is represented, and how the representation reduces the file size.

  This gives a precise explanation rather than simply naming the technique, and it helps demonstrate understanding of the principles of RLE and dictionary-based compression.

• Compare security precisely

  When comparing Caesar, computationally secure ciphers and Vernam ciphers, distinguish between a small key space, practical difficulty of breaking a cipher, and mathematically proved perfect security.

  The specification requires students to understand that Vernam is the only type listed with mathematically proved complete security, while other ciphers rely on computational security.