Information media: what they are
An information medium is the form that carries a message from a sender to a receiver. The four basic kinds are text (written words), pictures (photos, drawings, charts), sound (speech, music) and video (moving pictures, often with sound).
Each medium is good at something. Text is exact and easy to search. Pictures show shape and colour fast. Sound shows tone and feeling. Video shows change over time. Mass media such as newspapers, radio, TV and websites reach many people, while a phone call reaches one.
Today almost all media are stored and sent in digital form. That is why we study digitisation next.
Digitisation: turning media into numbers
The real world is analogue: sound pressure and light change smoothly. A computer can only store numbers, so it must digitise.
Sampling: measure the wave at equal gaps of time. Each measure is a sample. The number of samples per second is the sampling rate. Quantising: round each sample to the nearest whole number the computer can store. The number of bits per sample is the bit depth.
A picture is digitised by dividing it into tiny squares called pixels, and storing a colour number for each pixel. Video is a quick series of pictures (frames) plus sound.
Quality and size: more samples, or more pixels, copy the original better but need more storage. File size = number of samples × bits per sample. Compression makes files smaller by removing repeated or hard-to-notice data.
Expressive techniques
Expression means shaping a message so the receiver understands it quickly and feels what you want. You are not changing the message, only how it is shown.
Useful tools: size (big for the main point, small for details), contrast (dark on light or white on red, never pale on pale), icons and pictures (a symbol can replace many words), layout (group related things, leave space), and motion or sound (use sparingly to draw attention, and never make it the only way to get the message).
Match the medium to the job. A map is better as a picture, a rule as text, a tune as sound, a science experiment as video. Always think of the receiver: a clear message for a child, a poster seen from far away, or a person who cannot see colours.
Try it: one message, two ways
In the 3D, go to the last step. Switch on big letters, then strong colour, then icon, one at a time, and watch the clarity number. Which switch helps most? Next, move the sample slider from 4 to 32 and read how the numbers and bits change.
At home: write "Wash your hands" on two cards. Make one plain and one with big letters, a strong colour and a small drawing. Show both to a friend from 3 metres away. Which can they read?
Key formulas and definitions
- File size (bits) = number of samples × bits per sample
- Sampling rate = samples per second (hertz)
- Picture size (bits) = pixels × bits per pixel
- More samples/pixels → better quality, bigger file
Worked examples
1. A sound is sampled 8,000 times each second and each sample uses 8 bits. How many bits are stored for 1 second?
8,000 × 8 = 64,000 bits (which is 8,000 bytes).
2. Find the size of a 10-second clip using the same sampling (8,000 samples/s, 8 bits).
1 second = 64,000 bits, so 10 seconds = 640,000 bits = 80,000 bytes.
3. A black-and-white picture is 100 pixels wide and 50 pixels tall, using 1 bit per pixel. How many bits?
Pixels = 100 × 50 = 5,000. Bits = 5,000 × 1 = 5,000 bits.
4. If we double the samples per second, what happens to quality and file size?
Quality gets closer to the real wave, and the file size doubles.
5. A poster has thin grey letters on a white wall. Suggest three changes using expressive techniques.
Make the letters much bigger (size), change to black or dark red on white (contrast), and add a simple icon beside the main word (icon).
6. A picture is 200 × 100 pixels with 8 bits per pixel. Find its size in bytes.
Pixels = 20,000. Bits = 20,000 × 8 = 160,000. Bytes = 160,000 ÷ 8 = 20,000 bytes.
Common mistakes
- Thinking digital sound is a smooth wave. It is a list of numbers, and the smoothness is only close copying.
- Believing more samples always means a smaller file. More samples mean a bigger file.
- Using pale colours on a pale background because it looks soft. The message becomes hard to read.
- Adding too much motion and sound. Too many effects hide the message instead of showing it.