← IGCSE Computer Science Paper 1

Digital camera

Input device: a lens focuses light onto an image sensor of light-sensitive cells; each cell becomes a pixel of digital data, stored as an image file. More pixels give more detail.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 6

Understanding Digital camera in IGCSE Computer Science Paper 1

What it does: The data from each cell is stored as one pixel, so a sensor with more cells gives an image with more pixels. The lens bends and focuses incoming light so a sharp image falls on the image sensor. Storing the file happens later, after the sensor has captured the light. More pixels means the scene is split into smaller pieces, so more fine detail can be shown. A digital camera captures light from the real world and turns it into digital data for a computer to process, so it is an input device. Detail increases with the number of pixels, so a camera with fewer pixels captures less detail.

Common mistakes: The lens focuses the light onto the image sensor. The sensor does not focus light. The line should be lens.focus(light, sensor). The light-sensitive cells are in the image sensor, not in the lens. The loop should be FOR EACH cell IN sensor.

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Learning
Duo
What does the lens of a digital camera do?
It focuses light onto the image sensorIt stores the photo as a file
Matches
The lens turns light into digital data.
↓
It is the image sensor that turns light into digital data. The lens only focuses the light onto the sensor.
Applying
Meanings
Term
digital camera
Meaning
Input device: a lens focuses light onto an image sensor of light-sensitive cells; each cell becomes a pixel of digital data, stored as an image file. More pixels give more detail.
Practice
light ← lens.focus(light)
Testing
Gaps
light ← .FOCUS(scene)
Check Answer
Spots
1light ← scene.reflect()
2sensor.focus(light, lens)

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Quick Questions

1. What does the lens of a digital camera do?
A. It focuses light onto the image sensor ✓
B. It stores the photo as a file
The lens bends and focuses incoming light so a sharp image falls on the image sensor. Storing the file happens later, after the sensor has captured the light.
2. What is the image sensor made of?
A. One large microphone
B. Many light-sensitive cells ✓
The image sensor is a grid of tiny light-sensitive cells. Each cell records the light that falls on it.
3. What does each light-sensitive cell on the image sensor become in the final picture?
A. One pixel ✓
B. One whole image file
Each cell records brightness and colour for one point of the image, which becomes one pixel. Many pixels together make the whole image.
4. What does a cell on the image sensor record?
A. The brightness and colour of the light that hits it ✓
B. The sound waves that hit it
Cells detect light, not sound. Brightness and colour are turned into digital data for each pixel.
5. Which picture has more detail?
A. An image made of fewer pixels
B. An image made of more pixels ✓
More pixels means the scene is split into smaller pieces, so more fine detail can be shown.

Match the Pairs

lens → The part of a digital camera that focuses light onto the image sensor
image sensor → A chip made of many light-sensitive cells that record brightness and colour and turn light into digital data
Each light-sensitive cell on the image sensor becomes one pixel of the final image → 1 cell = 1 pixel
More pixels give more detail, but the image file needs more storage space → 12 megapixels > 2 megapixels
The lens turns light into digital data. → It is the image sensor that turns light into digital data. The lens only focuses the light onto the sensor.
Fewer pixels give a more detailed picture. → More pixels, not fewer, give a more detailed picture, because each pixel records a smaller part of the scene.

Key Term

digital camera
Input device: a lens focuses light onto an image sensor of light-sensitive cells; each cell becomes a pixel of digital data, stored as an image file. More pixels give more detail.

Fill in the Blanks

1. light ← lens.FOCUS(scene)
Hint: Type the camera part that focuses light from the scene.
2. data ← image_sensor.CAPTURE(light)
Hint: Type the part made of many light-sensitive cells that turns light into digital data.
3. FOR EACH cell IN sensor pixel ← cell.READ() NEXT cell
Hint: Type the name of the single light-sensitive unit on the sensor that becomes one pixel.
4. SAVE(image, "photo.jpg")
Hint: Type the command that stores the image as a file.
5. IF pixels > 1000000 THEN detail ← "high" ENDIF
Hint: Type the comparison operator meaning 'more than', because more pixels give more detail.

Spot the Error

Question 1
A light ← scene.reflect()
B sensor.focus(light, lens)
C data ← sensor.convert(light)
Line B — The lens focuses the light onto the image sensor. The sensor does not focus light. The line should be lens.focus(light, sensor).
Question 2
A FOR EACH cell IN lens
B pixel ← cell.read()
C image.add(pixel)
D NEXT cell
Line A — The light-sensitive cells are in the image sensor, not in the lens. The loop should be FOR EACH cell IN sensor.
Question 3
A camA ← 12000000
B camB ← 2000000
C IF camA < camB THEN
D OUTPUT "camA more detail"
Line C — camA has more pixels than camB, so it gives more detail. The condition must be camA > camB, otherwise the output message is wrong.
Question 4
A cell ← sensor.cell(1)
B pixel ← cell.read()
C image.add(lens)
Line C — Each sensor cell becomes a pixel, and the pixels make up the image. A lens is not a pixel, so the line should be image.add(pixel).
Question 5
A photo ← camera.capture()
B photo.name ← "IMG_001.jpg"
C memoryCard.delete(photo)
Line C — The image is stored as a file on the memory card. It must be saved, not deleted. The line should be memoryCard.save(photo).

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