Compression Practice Questions

Question 1

A 10×10 pixel image uses 4 bits per pixel. If the image is compressed using lossless compression, what can be said about the compressed file size?

Accepted Answer

It will be less than or equal to 50 bytes. — Uncompressed size = 10×10×4 bits = 400 bits = 50 bytes. Lossless compression reduces file size without losing data, so the compressed size will be less than or equal to the original. It could be equal if the data is incompressible, but not greater.

Question 2

A student records a sound using a microphone and stores it as a digital file. The file is then compressed using lossy compression. Which of the following is the most likely consequence?

Accepted Answer

The file size decreases, but some audio information is permanently lost. — Lossy compression reduces file size by discarding data that is less perceptible to human hearing. This results in a loss of quality that is often imperceptible but permanent. Lossless compression would allow perfect reconstruction, but lossy does not.

Question 3

Which of the following is a disadvantage of using lossy compression for images?

Accepted Answer

It permanently reduces image quality. — Lossy compression reduces file size by discarding some data, which can degrade image quality. This loss is permanent; the original quality cannot be restored. The other options are not typical disadvantages of lossy compression.

Question 4

Which of the following is a disadvantage of using lossy compression for images?

Accepted Answer

It permanently removes some data, which can reduce image quality. — Lossy compression reduces file size by discarding some data, which can cause a loss of quality that may be noticeable. It is commonly used for photographs where some loss is acceptable.

Question 5

A digital audio file is compressed using lossy compression. Which of the following is a consequence of this?

Accepted Answer

Some audio data is permanently discarded, potentially reducing sound quality. — Lossy compression removes data that is less perceptible to human hearing, resulting in smaller file sizes but irreversible loss of information. This can degrade quality, especially at high compression ratios.

Question 6

Which of the following is a disadvantage of using lossy compression for images?

Accepted Answer

It permanently removes some data, reducing image quality. — Lossy compression reduces file size by discarding some data that is considered less important, which can degrade quality. It does not increase file size; it decreases it. It is commonly used for photographs (e.g., JPEG). Decompression is generally fast, and the processing power is not a major disadvantage.

Compression

Subtopics in this area

Compression Revision Guide

Learning Objectives

Sample Exam Questions

Related Topics in OCR GCSE Computer Science

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Boolean logic

Programming fundamentals

Primary storage (memory)