Text, Sound & Images

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Lesson notes

Character Sets

A character set is all characters and symbols a computer can represent; each character has a unique binary code.
Character sets are ordered logically (e.g., code for 'B' is one more than code for 'A').
They provide a standard for computers to communicate; without one, the same binary code could be interpreted differently.
The number of representable characters = 2^(number of bits used).
Two common character sets: ASCII (7-bit, 128 characters) and UNICODE (minimum 16-bit, 65,536+ characters).
ASCII covers English letters, digits, and some symbols; cannot represent other languages or emojis.
Extended ASCII uses 8 bits (256 characters), adding mathematical operators and symbols like ©.
UNICODE supports characters from all major languages and special symbols like emojis; uses more storage than ASCII.

Representing Sound – Sampling

Sound is originally analogue; it must be converted to digital via Analogue-to-Digital conversion (A2D).
The process measures the amplitude of the sound wave at regular intervals; each measurement is a sample.
Each sample is stored as a binary value; the collection of samples forms a digital representation of the wave.
The digital wave can be stored on secondary storage and played back by reversing the process.

Sample Rate and Sample Resolution

Sample rate is the number of samples taken per second, measured in Hertz (Hz) (1 Hz = 1 sample/second).
Higher sample rate → digital wave closer to original → better quality, but larger file size.
A typical audio CD uses a sample rate of 44.1 kHz (44,100 samples per second).
Sample resolution (or bit depth) is the number of bits stored per sample.
Higher sample resolution → more possible amplitude values → better quality, but larger file size.
Both high sample rate and high sample resolution increase playback quality and file size.

Bitmap Images

A bitmap image is made up of a grid of pixels (picture elements).
A pixel is the smallest element of a bitmap image; each pixel is stored as a binary code representing its colour.
More colours and more detail → higher quality → more binary data needed.

Resolution and Colour Depth

Resolution is the total number of pixels in an image, calculated as width × height (in pixels).
Higher resolution → more detail → larger file size.
Colour depth is the number of bits used per pixel; determines the number of possible colours (2^colour depth).
Examples: 1-bit → 2 colours (black & white); 8-bit → 256 colours; 24-bit → 16.7 million colours (True Colour).
Higher colour depth → more colours → larger file size.
File size = width × height × colour depth (in bits).
A balance between quality and file size must be considered.

Analogue sound wave (blue) sampled at regular intervals to produce a digital wave (red). Vertical dashed lines show sample points.

A bitmap image is a grid of pixels; each pixel stores a binary code representing its colour.

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Practice questions

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1.What is a character set?
Easy
- AAll the characters and symbols that can be represented by a computer system
- BA set of instructions for encoding images
- CA collection of fonts used in word processing
- DA standard for compressing text files
2.How many bits does standard ASCII use to represent a character?
Easy
- A7 bits
- B8 bits
- C16 bits
- D32 bits
3.Which character set can represent characters from all major languages around the world?
Easy
- AASCII
- BExtended ASCII
- CUNICODE
- DEBCDIC
4.If an image has a resolution of 100 × 100 pixels and a colour depth of 4 bits, how many bits are needed to store the image?
Medium
- A10,000 bits
- B40,000 bits
- C100,000 bits
- D400,000 bits
5.What is the sample rate of a typical audio CD?
Easy
- A44.1 kHz
- B22.05 kHz
- C96 kHz
- D192 kHz
6.Which of the following is a benefit of using UNICODE over ASCII?
Easy
- AUNICODE uses fewer bits per character
- BUNICODE can represent emojis and symbols from many languages
- CUNICODE is faster to process
- DUNICODE requires less storage space
7.A sound recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. If the recording is 10 seconds long, what is the approximate file size in bits? (Ignore any compression or header.)
Medium
- A7,056,000 bits
- B44,100 bits
- C705,600 bits
- D441,000 bits
8.An image has a colour depth of 24 bits. How many different colours can it represent?
Easy
- A256
- B65,536
- C16,777,216
- D24

More questions

9.Which of the following best describes the relationship between sample rate and file size for a digital audio recording?
Easy
- AHigher sample rate leads to smaller file size
- BHigher sample rate leads to larger file size
- CSample rate does not affect file size
- DSample rate affects quality but not file size
10.A bitmap image is 1920 pixels wide and 1080 pixels high with a colour depth of 8 bits. What is the file size in bytes?
Medium
- A2,073,600 bytes
- B16,588,800 bytes
- C2,073,600 bits
- D16,588,800 bits
11.A student records a sound at a sample rate of 22 kHz and a sample resolution of 8 bits. They then re-record the same sound at 44 kHz and 16 bits. Which statement is correct?
Medium
- AThe second recording has higher quality and smaller file size
- BThe second recording has higher quality and larger file size
- CThe second recording has lower quality and smaller file size
- DThe second recording has lower quality and larger file size
12.Which of the following is an advantage of using ASCII over UNICODE?
Easy
- AASCII can represent more characters
- BASCII uses less storage space per character
- CASCII supports emojis
- DASCII can represent characters from all languages
13.A bitmap image has a width of 800 pixels and a height of 600 pixels. The colour depth is 24 bits. What is the file size of the image in bytes?
Medium
- A1,440,000 bytes
- B11,520,000 bytes
- C480,000 bytes
- D3,840,000 bytes
14.A digital audio recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. If the recording is 10 seconds long, what is the approximate file size in bits?
Medium
- A7,056,000 bits
- B441,000 bits
- C7,056,000 bytes
- D44,100 bits
15.What is the colour depth of a bitmap image that can represent 256 different colours?
Easy
- A8 bits
- B16 bits
- C4 bits
- D1 bit
16.A student captures an image using a camera with a resolution of 1920 × 1080 pixels and a colour depth of 24 bits. The image is then compressed using lossy compression. Which of the following is most likely to be the file size of the compressed image?
Hard
- A500 KB
- B6 MB
- C20 MB
- D2 GB
17.An image has a colour depth of 4 bits. How many different colours can it represent?
Easy
- A16
- B8
- C32
- D4
18.A sound file has a sample rate of 22 kHz and a sample resolution of 8 bits. The file is 5 seconds long. What is the file size in bytes?
Medium
- A110,000 bytes
- B880,000 bytes
- C22,000 bytes
- D1,760,000 bytes
19.What is the smallest element of a bitmap image?
Easy
- APixel
- BColour depth
- CResolution
- DByte
20.A bitmap image is 100 pixels wide and 100 pixels high. The colour depth is 1 bit. What is the file size in bytes?
Medium
- A1250 bytes
- B10,000 bytes
- C100 bytes
- D1,250,000 bytes
21.A digital audio recording has a sample rate of 48 kHz and a sample resolution of 16 bits. How many bits of data are recorded per second?
Medium
- A768,000 bits
- B48,000 bits
- C768,000 bytes
- D3,000 bits
22.An image has a resolution of 1920 × 1080 pixels and a colour depth of 8 bits. What is the file size in bytes?
Medium
- A2,073,600 bytes
- B16,588,800 bytes
- C259,200 bytes
- D20,736,000 bytes
23.A bitmap image has a resolution of 800 × 600 pixels and a colour depth of 8 bits. What is the file size in bytes?
Medium
- A480,000 bytes
- B3,840,000 bytes
- C60,000 bytes
- D384,000 bytes
24.If an image has a colour depth of 4 bits, how many different colours can it represent?
Easy
- A4
- B8
- C16
- D256
25.A sound recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. If the recording is 10 seconds long, what is the approximate file size in bits?
Medium
- A7,056,000 bits
- B7,056,000 bytes
- C705,600 bits
- D44,100 bits
26.An image has a resolution of 1920 × 1080 pixels and a colour depth of 24 bits. What is the file size in bytes?
Medium
- A6,220,800 bytes
- B49,766,400 bytes
- C2,073,600 bytes
- D16,588,800 bytes
27.A bitmap image is 800 pixels wide and 600 pixels high with a colour depth of 8 bits. What is the file size in bytes?
Medium
- A480,000 bytes
- B3,840,000 bytes
- C384,000 bytes
- D480 bytes
28.A bitmap image has a colour depth of 8 bits. How many different colours can it represent?
Easy
- A256
- B8
- C16
- D128
29.A sound recording is sampled at 44.1 kHz with a sample resolution of 16 bits. The recording is 30 seconds long. What is the approximate file size in bits?
Medium
- A21,168,000 bits
- B1,323,000 bits
- C211,680 bits
- D10,584,000 bits
30.An image has a resolution of 800 × 600 pixels and a colour depth of 24 bits. What is the file size in bytes?
Medium
- A1,440,000 bytes
- B11,520,000 bytes
- C480,000 bytes
- D192,000 bytes
31.What is the term for the number of samples taken per second when digitising sound?
Easy
- ASample rate
- BSample resolution
- CBit depth
- DFrequency
32.A student records a sound at a sample rate of 22 kHz and a sample resolution of 8 bits. The file size is 1.76 million bits. How long is the recording in seconds?
Hard
- A10 seconds
- B20 seconds
- C8 seconds
- D5 seconds
33.Which of the following best describes the effect of increasing the sample rate of a digital audio recording?
Easy
- AThe file size increases and the playback quality improves
- BThe file size decreases and the playback quality improves
- CThe file size increases and the playback quality worsens
- DThe file size decreases and the playback quality worsens
34.A student captures an image using a camera with a resolution of 1920 × 1080 pixels and a colour depth of 24 bits. The image is then compressed using lossy compression. Which of the following is most likely to happen?
Medium
- AThe file size decreases and image quality may be reduced
- BThe file size increases and image quality improves
- CThe file size decreases and image quality improves
- DThe file size increases and image quality may be reduced
35.A student records a sound at a sample rate of 22 kHz and a sample resolution of 8 bits. The recording lasts 10 seconds. What is the file size in bits?
Medium
- A1,760,000 bits
- B2,200,000 bits
- C1,760,000 bytes
- D2,200,000 bytes
36.Which of the following is the smallest element of a bitmap image?
Easy
- APixel
- BBit
- CByte
- DColour depth
37.An image has a resolution of 800 × 600 pixels and a colour depth of 8 bits. What is the file size in bytes?
Medium
- A480,000 bytes
- B3,840,000 bytes
- C60,000 bytes
- D480,000 bits
38.A digital audio recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. The recording is 30 seconds long. How many bits are stored?
Medium
- A21,168,000 bits
- B21,168,000 bytes
- C1,323,000 bits
- D1,323,000 bytes
39.How many different colours can be represented in an image with a colour depth of 4 bits?
Easy
- A16
- B8
- C4
- D2
40.A bitmap image has a width of 1920 pixels and a height of 1080 pixels. The colour depth is 24 bits. What is the file size in bytes?
Medium
- A6,220,800 bytes
- B49,766,400 bytes
- C6,220,800 bits
- D49,766,400 bits
41.ASCII uses 8 bits to represent each character.
Easy
True or false?
42.How many characters can standard ASCII represent?
Easy
- A128
- B256
- C65,536
- D16
43.Increasing the sample rate of a digital audio recording increases the file size but improves playback quality.
Easy
True or false?
44.Which of the following is a benefit of UNICODE over ASCII?
Easy
- AUses less storage space
- BCan represent characters from all major languages
- CUses 7 bits per character
- DIs easier to implement in hardware
45.Put the following steps in the correct order for digitising sound:
Medium
- Store the binary values on secondary storage
- Measure the amplitude of the analogue sound wave at regular intervals
- Convert each measurement into a binary value
- Play back the digital sound by reversing the process
46.Match each term to its correct description:
Medium
- Sample rate
- Sample resolution
- Colour depth
- Resolution
- Number of bits per sample
- Number of samples per second
- Number of bits per pixel
- Total number of pixels in an image
47.Match each term to its correct description.
Medium
- Sample rate
- Sample resolution
- Analogue to Digital conversion
- Number of bits stored per sample
- Number of samples taken per second
- Process of converting sound wave to digital form
48.Arrange the following steps in the correct order for digitising sound.
Medium
- Store the binary values on secondary storage
- Measure the amplitude of the analogue wave at regular intervals
- Convert each measurement to a binary value
- Play back the digital wave by reversing the process
49.Which of the following are true about UNICODE compared to ASCII? (Select all that apply)
Medium
- AUNICODE uses fewer bits per character
- BUNICODE can represent characters from multiple languages
- CUNICODE uses at least 16 bits per character
- DUNICODE is backward compatible with ASCII
- EUNICODE cannot represent emojis
50.A bitmap image with a colour depth of 8 bits can represent up to 256 different colours.
Easy
True or false?
51.Complete the sentence.
Easy
The process of converting an analogue sound wave into a digital form is called ____.
52.A bitmap image has a colour depth of 4 bits. How many different colours can it represent?
Easy
53.State one advantage of using ASCII over UNICODE.
Medium
54.A sound recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. How many bits of data are recorded in one second?
Medium
55.A bitmap image has a resolution of 640 × 480 pixels and a colour depth of 16 bits. Calculate the file size in bytes.
Medium
56.Define the term 'pixel'.
Easy
57.A bitmap image has a colour depth of 4 bits. How many different colours can it represent?
Easy
- A15
- B18
- C16
- D17
58.A sound recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. How many bits of data are recorded in one second?
Medium
- A635040 bits
- B776160 bits
- C846720 bits
- D705600 bits
59.A bitmap image has a resolution of 640 × 480 pixels and a colour depth of 16 bits. Calculate the file size in bytes.
Medium
- A614400 bytes
- B552960 bytes
- C675840 bytes
- D737280 bytes

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