Representing sound, images and text digitally
Photos, songs and messages all end up as the same thing inside a computer: streams of binary digits.
Part of your national curriculum
- Data and representation: Understand how sound, images and text can be represented and manipulated in a digital form
Lesson overview
What you'll learn in this lesson
Understand how sound, images and text can be represented and manipulated in a digital form
Key learning points
- • Images as pixels
- • Sound as samples
- • Text as character codes
This lesson at a glance
- 28 minutes
- 14 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 14
Watch first
Representing sound, images and text digitally
An English teaching video on this topic from Prototype Education. Watch it, then scroll down for the lesson.
In a nutshell
Understand how sound, images and text can be represented and manipulated in a digital form
Learning cycle
Part 2 of 14
Learning cycle 1 of 2
Part 1 · Images as pixels
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 14
Learn
Images as pixels
A digital image is a grid of pixels, each stored as numbers for red, green and blue (RGB), often 8 bits each, giving 256 shades per colour and about 16.7 million combinations. A 100x100 pixel image needs 10,000 pixels' worth of data.
Explore the idea
Part 4 of 14
Learn
Sound as samples
Sound is sampled thousands of times per second; CD audio samples 44,100 times a second (44.1 kHz), storing the wave's height as a number each time. More samples per second, and more bits per sample, capture finer detail but need more storage.
Quick check
Part 5 of 14
Quick check
What three values usually describe one pixel's colour?
Reset break
Part 6 of 14
Pause
That's sitting 1 of 2 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 7 of 14
Quick check
CD audio samples sound how many times per second?
Learning cycle
Part 8 of 14
Learning cycle 2 of 2
Part 2 · Text as character codes
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 9 of 14
Learn
Text as character codes
Every character has a number: Unicode assigns 'A' the code 65, and 'a' the code 97. A text file is really just a sequence of these numbers, converted back into letters on screen by the software reading it.
Quick check
Part 10 of 14
Quick check
What is stored for the character 'A' in a text file?
Challenge round
Part 11 of 14
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 12 of 14
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
A ____ image is a grid of pixels, each stored as numbers for red, green and blue (RGB), often 8 bits each, giving 256 shades per colour and about 16.7 million combinations.
A 100x100 pixel image needs 10,000 ____' worth of data.
Mastery quiz
Part 13 of 14
Marked quiz
End of lesson quiz: Representing sound, images and text digitally
3 questions, marked with the reasoning shown. No timer.
1. What three values usually describe one pixel's colour?
2. CD audio samples sound how many times per second?
3. What is stored for the character 'A' in a text file?
Lesson round-up
Part 14 of 14
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
How a supermarket checkout knows the price
When a barcode is scanned, the checkout does not store the price itself. It sends the barcode number to a database and reads back a record: product name, price, whether it needs an age check. The record is the single place the price lives, so changing one row changes every till in the shop at once.
Problems come from bad data, not bad scanners. If two products share a barcode, or a price update reaches the shop overnight but the till holds an old copy in its cache, customers are charged the wrong amount. Shops check this with test transactions: scan a known item, expect a known price, record what actually happened.
Good systems also log every scan. If a customer complains, the log shows exactly which record was used and when.
Written for Good Learning Co.
Reading questions
- Write in your own words what the checkout sends and what it receives back.
- Explain one way bad data could cause a wrong price, and how logging helps find it.
- Design a test table with four tests for a new checkout, with expected and actual results.
Reading and notes
ReadingRead the lesson text again and note the key terms and how each one is used, in your own words — as you would for revision.
Half a page of notes
Extended writing
WritingExplain a real system that uses this idea — how it works, where it can go wrong, and how you would make it safer or better.
250–350 words
Algorithm on paper
DiagramWrite your steps out as pseudocode or a flowchart before you type anything, then photograph it.
1 flowchart or 10 lines
Code write-up
WritingCopy your code in, then explain underneath what each part does and what you had to fix.
Code + 5 sentences
Test table
Working outMake a test table: what you tried, what you expected, what actually happened.
4–6 tests
Saved as you type.
Part 1 of 14 · Watch & discover
How this is going
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Understand how sound, images and text can be represented and manipulated in a digital form