Data representation: images and sound

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Explain how pixel coordinates and colour codes represent a bitmap
Decode a small black-and-white image and identify what metadata is needed

Vocabulary: bitmap · pixel · coordinate · bit depth · metadata

Retrieve previous learning

What values can one binary digit store?

Check: One bit has two possible values, 0 and 1.

Learn the concept

A bitmap records a rectangular grid of picture elements called pixels. To decode a sequence of pixel values, the reader must know the grid width, height, order and colour interpretation. In a one-bit classroom example, let 0 mean white and 1 mean black; actual file formats also specify their own encoding and metadata.

Read rows left to right, top to bottom. The twelve-bit pattern 010 / 111 / 101 / 101 is a four-row, three-column image if the rows are separated as shown. Its first row has a black centre pixel, and its second row is entirely black. The same twelve bits could form a different picture at width four, which shows why dimensions matter.

One bit per pixel offers two coded values, not necessarily black and white unless the palette says so. With n bits per pixel, up to 2^n distinct codes can be represented. A four-pixel row at two bits per pixel could encode 00, 01, 10, 11: four codes, whose visible colours still depend on the palette. Use an original pixel drawing and add text that conveys essential information.

Worked model

Declare a three-column by four-row grid with 0 white and 1 black.
Split 010111101101 into four groups: 010, 111, 101, 101.
Plot each group on its own row and check the count is 3 × 4 = 12 pixels.
Record dimensions, row order and palette alongside the bits so another person can decode the same image.

Guided practice

Decode 101 / 010 for a three-column, two-row grid where 1 is black.

Hint: Draw two rows in the stated order.

Check the guided answer

The first row has black pixels at left and right; the second has a black centre pixel. There are six pixels and six bits.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“The pixel bit string alone always defines the displayed picture.”

Correction: Dimensions, order and palette determine how those bits become a grid and visible colours.

Extend and reflect

How many distinct codes can three bits per pixel represent?

Guidance: Calculate 2³ = 8 codes; a format's palette determines their colours, and a larger code count does not create extra pixels.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Explain how pixel coordinates and colour codes represent a bitmap. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Data representation · original lesson pack

DASKEREL beta · internal AI review pending

Estimate the raw size of a bitmap image

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Relate width, height and colour depth to raw bit count
Distinguish raw estimate from a real compressed file

Vocabulary: pixel · resolution · colour depth · bit · compression

Retrieve previous learning

How many bits are in a byte?

Check: Eight bits make one byte.

Learn the concept

A bitmap samples an image on a grid. Width multiplied by height gives pixel count; multiplying by bits per pixel gives the raw pixel-data bit count. A 100 by 50 image with 24 bits per pixel has 5,000 pixels and 120,000 bits, or 15,000 bytes of raw pixel data.

A real PNG or JPEG file is not generally exactly that size. Headers, metadata and compression affect its stored bytes, and some formats use other channel arrangements. This classroom formula is an uncompressed pixel-data estimate, not a promise about a particular export.

Higher dimensions or colour depth can increase raw data but may or may not visibly improve the intended result. Compare images at the actual display size, preserve rights and provide text alternatives for informative graphics. Do not treat a smaller file as automatically better if important information is lost.

Worked model

Calculate 100 × 50 = 5,000 pixels.
Multiply 5,000 × 24 = 120,000 raw bits.
Divide by 8 to get 15,000 raw bytes.
State that headers and compression can make the saved file size differ.

Guided practice

Estimate raw pixel bytes for a 10×10 image at 8 bits per pixel.

Hint: Multiply dimensions and bit depth, then divide by eight.

Check the guided answer

10×10×8 = 800 bits = 100 bytes of raw pixel data, before any file headers or compression.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“Raw pixel bytes always equal the size shown for a PNG file.”

Correction: Encoding, headers, metadata and compression change the saved size.

Extend and reflect

Compare the raw data size if width and height both double.

Guidance: Pixel count becomes four times as large at unchanged colour depth; actual compressed size need not scale exactly fourfold.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Relate width, height and colour depth to raw bit count. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Data representation · original lesson pack

DASKEREL beta · internal AI review pending

Manipulate an image while preserving meaning and access

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Distinguish crop, resize and colour adjustment effects
Evaluate a final image for integrity, rights and accessibility

Vocabulary: crop · resize · aspect ratio · contrast · export

Retrieve previous learning

What factors determine a bitmap's raw pixel-data estimate?

Check: Width × height × bits per pixel, divided by eight for bytes.

Learn the concept

A crop removes pixels outside a selected frame; a resize changes output dimensions. Neither action creates detail absent from the source. If a 1200×800 image is reduced proportionally to width 600, its height becomes 400 because both dimensions are halved. Forcing the height to 800 instead would stretch the image and distort shapes.

Adjustments such as brightness and contrast can improve legibility, but strong changes may erase dark or light detail. For an instructional diagram, inspect labels and boundaries at the intended display size. Keep the original so the edit can be compared and reversed. An image used as evidence must not be edited so that it misrepresents the event or result.

Plan purpose, rights and access before export. An informative image needs a concise text alternative describing its essential content; decorative images can be marked accordingly in the publishing tool. Use permission-cleared originals or licensed assets. The teacher should inspect both editable source and saved export rather than relying on a written claim that an edit worked.

Worked model

Copy an original 1200×800 school-approved diagram and note its purpose and rights.
Crop only a blank border if it hides no labels, then resize proportionally to 600×400 when the retained aspect ratio is 3:2.
Preview at intended size and compare labels, colour contrast and meaning against the original.
Export, reopen the file and provide an essential-content text description.

Guided practice

A 900×600 image is reduced proportionally to width 450. What height is needed?

Hint: The width scale factor is one half.

Check the guided answer

The proportional height is 300 pixels. Both dimensions halve, preserving the original 3:2 aspect ratio.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“Resizing a bitmap upward restores detail that was never captured.”

Correction: Interpolation can add pixels but cannot recover missing source detail; check the actual result rather than inferring quality from dimensions.

Extend and reflect

Compare a crop and a resize for a diagram with a caption at the bottom.

Guidance: A careless crop can remove the caption; a resize can make it too small. Explain which purpose each operation serves and inspect the exported result.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Distinguish crop, resize and colour adjustment effects. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Data representation · original lesson pack

DASKEREL beta · internal AI review pending

Sample sound and estimate raw audio data

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Explain sampling rate, bit depth and channels
Calculate a raw uncompressed audio estimate

Vocabulary: sample · sample rate · bit depth · channel · quantisation

Retrieve previous learning

What factors increase an image's raw pixel-data size?

Check: Pixel width, pixel height and bits per pixel.

Learn the concept

A microphone produces a changing signal. Digital recording samples its amplitude at regular times and represents each sampled value with a finite number of bits. Sample rate counts samples per second; bit depth counts bits per sample per channel. More samples or more bits can capture more detail, but quality also depends on the recording chain and task.

Raw uncompressed bits equal seconds × samples per second × bits per sample × channels. A five-second mono recording at 8,000 samples per second and 8 bits per sample has 5×8,000×8×1 = 320,000 bits = 40,000 bytes of sample data. Stereo doubles the channel factor if the other settings stay the same.

A real audio file can include headers and compression; a compressed format may have a very different size. Recording voices requires consent and school safeguarding rules. Use original non-personal sounds or generated examples, and provide a transcript or description for essential audio.

Worked model

Identify duration 5 s, rate 8,000 samples/s, depth 8 bits and mono 1 channel.
Multiply to obtain 320,000 raw bits.
Divide by eight to obtain 40,000 raw bytes.
Explain why a saved compressed file may not match that number.

Guided practice

How many raw bytes are two seconds of mono audio at 1,000 samples/s and 8 bits/sample?

Hint: Multiply seconds × rate × bit depth, then divide by eight.

Check the guided answer

2×1,000×8 = 16,000 bits = 2,000 raw bytes, before header or compression.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“A larger sampling rate changes the length of a recording.”

Correction: At fixed duration it increases samples captured per second and raw data size; playback length remains the same when interpreted correctly.

Extend and reflect

Compare the raw data effect of doubling sample rate and halving duration.

Guidance: Their product remains unchanged if depth and channels are fixed; content and quality implications still need separate discussion.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Explain sampling rate, bit depth and channels. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Data representation · original lesson pack

DASKEREL beta · internal AI review pending

Edit an original sound clip without losing its purpose

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Plan a trim, level and export for a named purpose
Check rights, consent and an accessible alternative

Vocabulary: waveform · trim · level · clip · export · transcript

Retrieve previous learning

What is a sample rate?

Check: The number of signal-amplitude samples recorded per second per channel.

Learn the concept

A waveform display shows changing sample amplitude over time; it does not show the meaning of speech by itself. For a fictional 12-second bell demonstration, a learner may trim two seconds of silence at the start and one at the end. The planned content length is then nine seconds, provided those intervals do not contain useful sound.

Adjust level to make the content audible without clipping. Flattened peaks or harsh distortion are warnings, but listen on approved headphones at a safe volume and inspect the exported file. Keep the original recording so edits can be reversed. A fade can avoid an abrupt cut, though it must not hide important information.

Do not record or share another person's voice without the school's consent process. Use original permission-cleared sounds and avoid copyrighted music unless licensed. If audio conveys essential information, provide a transcript or equivalent text. A teacher should observe the edit in the approved tool and check the actual result.

Worked model

Name the bell clip's intended purpose and retain its original file.
Mark the two-second opening silence and one-second closing silence on a copy.
Trim, preview levels without clipping and export a nine-second version.
Listen to the export and attach a short description or transcript as appropriate.

Guided practice

A 20-second clip loses 3 seconds at the start and 2 at the end. What duration remains?

Hint: Subtract both trims from the original.

Check the guided answer

20−3−2 = 15 seconds, assuming the removed intervals do not overlap and the export includes the full remainder.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“A waveform picture proves a voice recording is understandable.”

Correction: The waveform shows amplitude over time; meaning, clarity and accessibility require listening and text review.

Extend and reflect

Plan a reduced-noise revision without misrepresenting speech.

Guidance: Compare before and after, retain the original and avoid removing words or changing their meaning.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Plan a trim, level and export for a named purpose. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Data representation · original lesson pack

DASKEREL beta · internal AI review pending

Compare lossless and lossy compression

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Explain how compression changes storage size
Choose lossless or lossy methods for a stated purpose

Vocabulary: compression · lossless · lossy · quality · original

Retrieve previous learning

Why can a real file differ from a raw image or audio size estimate?

Check: It includes format information, may include metadata and may apply compression.

Learn the concept

Compression represents data in fewer bytes. Lossless compression can reconstruct the exact original data when decoded; lossy compression discards some information to achieve a smaller file. Neither label alone guarantees a given file size because content and settings matter.

An original line diagram with sharp text may need lossless export so edges remain clear. A photographic preview may tolerate a carefully chosen lossy setting, but inspect labels and important detail at final size. Repeatedly saving a lossy copy can compound quality loss, so retain an original source.

A reported ratio needs clear units. If a 4 MB file becomes 1 MB, its new size is 25% of the old and the reduction is 75%. Do not call this 'four times better quality'. Compare quality, access needs and rights alongside size. A smaller upload may be useful but does not justify omitting a transcript or text alternative.

Worked model

Define whether a fictional file is a text-heavy diagram or photographic preview.
Choose a suitable lossless or lossy candidate and export from the original source.
Compare 4 MB with 1 MB: ratio 4:1 and 75% size reduction.
Inspect the output for essential detail, retain the source and explain the trade-off.

Guided practice

A 10 MB file becomes 6 MB. What percentage size reduction is this?

Hint: Divide the 4 MB saved by the original 10 MB.

Check the guided answer

(10−6)/10 = 0.4, so the reduction is 40%. The quality effect cannot be inferred from size alone.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original image or audio edit in a school-approved tool, including save and export.
Learner shows the source and exported versions, explains one deliberate change and verifies rights to any imported material.
The result is checked at target quality and with an accessible equivalent where needed.

Find and correct a misconception

“All compression permanently deletes information.”

Correction: Lossless methods can reconstruct the original data exactly; lossy methods discard some information.

Extend and reflect

Compare two encodings of the same original image fairly.

Guidance: Keep dimensions and viewing conditions fixed, report actual size and inspect important details and access alternatives.