Quiz - Compression

Instructions

Answer all 15 questions to test your knowledge of data compression. You'll see your results at the end.

Topics covered: The need for compression, lossy vs lossless compression, common scenarios, advantages and disadvantages, effects on files

Question 1

What is the main purpose of compression?

To make files run faster To reduce file size for storage and transmission To encrypt files for security To convert files between formats

Explanation: Compression reduces file size by encoding data more efficiently, making files easier to store and faster to transmit over networks.

Question 2

Which of these is a scenario where compression is essential?

Streaming video over the internet Running calculations in a spreadsheet Typing a document Changing font size

Explanation: Streaming video requires massive data transfer. Without compression, a 2-hour movie could be over 100 GB - compression makes streaming practical.

Question 3

What is lossless compression?

Compression that permanently removes some data Compression where original data can be perfectly restored Compression that only works on text files Compression that makes files larger

Explanation: Lossless compression preserves all original data. When decompressed, the file is bit-for-bit identical to the original.

Question 4

What is lossy compression?

Compression that corrupts files Compression that always fails Compression that permanently removes some data to achieve smaller sizes Compression that only works on very old files

Explanation: Lossy compression permanently discards data that humans are unlikely to notice (like inaudible sounds or invisible details), achieving much higher compression ratios than lossless.

Question 5

Which file format uses lossless compression?

JPEG MP3 ZIP MP4

Explanation: ZIP is a lossless archive format. JPEG, MP3, and MP4 are all lossy formats for images, audio, and video respectively.

Question 6

Which file format uses lossy compression?

PNG FLAC JPEG GIF

Explanation: JPEG uses lossy compression for photographs. PNG, FLAC, and GIF all use lossless compression (though GIF is limited to 256 colours).

Question 7

Why must software and program files use lossless compression?

Lossy compression makes files too small Even one changed bit can corrupt the program and cause crashes Lossy compression is slower Programs are too large for lossy compression

Explanation: Program files must be bit-perfect. Any data loss, even a single bit, could cause the software to crash, behave incorrectly, or fail to run at all.

Question 8

What is an advantage of lossy compression over lossless?

Files can be perfectly restored Much higher compression ratios (smaller files) Works with all file types Better for text documents

Explanation: Lossy compression typically achieves 80-95% size reduction, compared to 20-50% for lossless. This is why media files like photos and music can be so much smaller.

Question 9

What is a disadvantage of lossy compression?

Files become too large Original quality cannot be recovered Only works on very small files Takes too long to compress

Explanation: The main disadvantage of lossy compression is that it permanently removes data. You cannot get the original quality back from a lossy compressed file.

Question 10

A file is 100 MB. With 75% compression, what is the compressed size?

75 MB 50 MB 25 MB 10 MB

Explanation: 75% compression means 75% is removed, leaving 25% of the original size. 100 MB × 0.25 = 25 MB.

Question 11

What is "generation loss"?

Files becoming outdated over time Quality degradation from repeatedly saving in lossy format Loss of files due to hardware failure Forgetting passwords for compressed files

Explanation: Generation loss occurs when a lossy file is edited and saved multiple times. Each save recompresses the data, discarding more information and accumulating quality loss.

Question 12

Which compression type should be used for a hospital's medical records?

Lossy - to save maximum storage space Lossless - data accuracy is critical for patient safety Either type would work equally well No compression should be used

Explanation: Medical records must be exact to ensure patient safety. Even small data loss could lead to misdiagnosis or treatment errors. Lossless compression preserves all data.

Question 13

Why do streaming services use lossy compression for videos?

Lossless video doesn't exist Users prefer lower quality video It makes files small enough to stream over internet connections Lossy compression is faster to play

Explanation: Uncompressed video is massive (a 2-hour film could be over 100 GB). Lossy compression (like H.264) can reduce this to a few GB while maintaining acceptable quality for viewing.

Question 14

What are compression artifacts?

Historical files found in archives Visible or audible flaws caused by aggressive lossy compression Error messages when compression fails Backup copies of compressed files

Explanation: Compression artifacts are visual or audio distortions that appear when lossy compression removes too much data. Examples include blocky areas in images or tinny sounds in audio.

Question 15

A graphic designer is editing a photo. To avoid generation loss, they should:

Save as JPEG after every edit Edit in a lossless format and only export to JPEG once at the end Use the lowest JPEG quality setting Delete the original file immediately

Explanation: To prevent generation loss, always work with lossless formats (like PNG or PSD) during editing. Only convert to JPEG once, as the final export step.

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