Topic Four (1.4): Multimedia

Introduction Icon.png Introduction

This topic links with binary numbers and how they are used in images and sound. It is very theoretical but does involve some calculation as you have to perform calculations to work out the file size for a bitmap image.

By the end of this topic you should be able to:

  • Show an understanding of how data for a bitmapped image is encoded.
  • Perform calculations to estimate the file size for a bitmap image.
  • Show an understanding of the effects of changing elements of a bitmap image on the image quality and file size.
  • Show an understanding of how data for a vector graphic is encoded.
  • Justify the use of a bitmap image or vector graphic for a given task.
  • Show an understanding of how sound is represented and encoded.
  • Show an understanding of the impact of changing the sampling rate and resolution.

Watch Icon.png Watch

WATCH – Representing Images in Binary (YouTube) Links to an external site.

This video explains how bitmap images are represented in binary, and covers the terms pixels, resolution, colour depth and metadata.

WATCH – Representing Sound in Binary (YouTube) Links to an external site.

WATCH – Analogue vs Digital Sound (YouTube) Links to an external site.

Read & Make Notes Icon.png Read and Make Notes

Read pages 17 to 21 of the textbook. Ensure you make some notes and list examples as you read through. In particular, use the worked example 1.04 to see how you can calculate the size of a bitmap file.

Read Icon.png Further Reading

READ – Graphic File Formats (nationalarchives.gov.uk) Links to an external site.

READ – Representing Text, Images and Sound (BBC bitesize) Links to an external site.

WATCH – How Do ADCs Work? (The Learning Circuit) Links to an external site.

Review Icon.png End of Topic Review

Work through exam style questions 2a, 2b, 3, 5a and 5b on pages 24 and 25.

You may check your answers using the Module 1 Exam style answer sheet.

CHECK - Textbook Answers

Top Tip Icon.png Top Tip

Ensure you understand the following before moving on to the next topic.

  • There are two defining quantities for a bitmap image: the colour depth defining the number of bits per pixel and the resolution defining the dimensions of the image matrix measured in pixels.
  • A pixel is the smallest individual element in an image, which can be thought of as a dot, small circle or square.
  • A pixel is defined by a binary code representing its colour.
  • Dimensions in a drawing list must be relative to the overall dimensions of the image.
  • The sampling rate defines precisely when measurements of amplitude are made.
  • The sampling rate should be in accordance with Nyquist’s theorem.
  • There is an approximation when the ADC converts the analogue signal to a binary value.
  • The approximation is closer if more bits are used for the code; that is, if the sampling resolution is improved.
  • File size increases with increasing sampling resolution and with increasing sampling rate, but this will improve quality.
  • File sizes are each dimension in its smallest unit multiplied (width x height x bit depth (in bits) or resolution (bits) x frequency (hz) x time (in seconds)) to get the size in bits.