📝 Data compression in multimedia (9 MCQs)

📖 From Data Communication and Networks • 28. Multimedia • 9 questions available

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What is Data compression in multimedia?

Data compression in multimedia is the process of reducing the size of audio, video, image, or text files by removing redundancy or less important information so that they can be stored more efficiently and transmitted faster over networks without exceeding bandwidth limits.

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📝 All Data compression in multimedia MCQs

Q1. If a lossless compression algorithm reduces a file size by 40%, what is the resulting compression ratio?

A.0.4

B.0.6 ✅

C.1.4

D.2

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: A 40% reduction means the compressed file is 60% of the original. The compression ratio is calculated as original size divided by compressed size, yielding $\\frac{1}{0.6}=0.6$ . Therefore, option B correctly represents the ratio.

Q2. Increasing the quantization step size in JPEG compression typically causes which combination of changes in image quality and file size?

A.Higher quality, larger size

B.Higher quality, smaller size

C.Lower quality, larger size

D.Lower quality, smaller size ✅

💡 Difficulty: medium | ✅ Correct: D

📖 Explanation: Larger quantization steps coarsen the representation of frequency coefficients, discarding more detail. This reduces perceptual quality, producing a blurrier image, while simultaneously decreasing the amount of data needed to store the coefficients, resulting in a smaller file size. Hence, lower quality with smaller size is correct.

Q3. Codec X achieves a PSNR of 35 dB at 2 Mbps, while Codec Y achieves 33 dB at 1.5 Mbps. For a streaming service limited to 3 Mbps, which codec provides the best trade‑off between quality and bandwidth?

A.Codec X ✅

B.Codec Y

C.Both equally

D.Neither suitable

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Codec X delivers higher visual quality (35 dB) and still operates well below the 3 Mbps ceiling, using 2 Mbps. Codec Y, although lower bitrate, provides lower quality (33 dB) and does not offer a significant advantage. Therefore, Codec X offers the superior balance of quality and bandwidth within the constraint.

Q4. Which statement correctly distinguishes lossless from lossy compression?

A.Lossless always yields smaller files than lossy.

B.Lossy can be perfectly reconstructed, lossless cannot.

C.Lossless removes redundant data only, lossy removes perceptually irrelevant data. ✅

D.Lossless uses transform coding, lossy uses only Huffman coding.

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Lossless techniques preserve every original bit by eliminating only statistical redundancy, allowing exact reconstruction. Lossy methods intentionally discard information that is less noticeable to human perception, achieving higher compression at the cost of irreversible loss. The correct distinction is captured by option C.

Q5. When choosing between MP3 and FLAC for archiving music, which factor is most important for preserving audio fidelity?

A.MP3’s lower bitrate

B.MP3’s widespread support

C.FLAC’s larger file size

D.FLAC’s lossless nature ✅

💡 Difficulty: medium | ✅ Correct: D

📖 Explanation: FLAC stores audio without any loss of information, guaranteeing that the archived file is identical to the original source. MP3 compresses by removing detail, which degrades fidelity. Therefore, the decisive factor for preserving fidelity is FLAC’s lossless nature, as stated in option D.

Q6. Considering dictionary‑based methods, how does Huffman coding differ from LZW in terms of dictionary construction and typical data suitability?

A.Huffman uses dynamic dictionary, LZW uses static frequencies.

B.Both use identical dictionaries.

C.Huffman is only for image data, LZW only for audio.

D.Huffman builds a static tree based on symbol frequencies; LZW builds a dynamic dictionary of substrings, making LZW better for repetitive patterns like text. ✅

💡 Difficulty: hard | ✅ Correct: D

📖 Explanation: Huffman creates a fixed prefix tree derived from symbol frequencies, assigning shorter codes to more common symbols. LZW, by contrast, constructs a dictionary on‑the‑fly, adding new substrings as data are processed, which excels with repetitive sequences typical in text. Option D accurately describes these differences.

Q7. Applying Run‑Length Encoding (RLE) to a monochrome bitmap with long runs of identical pixels primarily reduces which type of redundancy?

A.Temporal redundancy

B.Spectral redundancy

C.Spatial redundancy ✅

D.Entropy redundancy

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: RLE compresses sequences of identical adjacent pixels by representing the run length and value once, eliminating repeated storage of the same pixel. This targets spatial redundancy, where neighboring pixels share the same color, making option C the correct answer.

Q8. How does the Discrete Cosine Transform (DCT) enable efficient lossy compression in video codecs?

A.It directly removes redundant frames.

B.It concentrates energy into a few low‑frequency coefficients, allowing high‑frequency components to be quantized heavily. ✅

C.It eliminates all frequencies above a threshold.

D.It replaces pixel values with binary codes.

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The DCT converts spatial pixel values into frequency coefficients, concentrating most of the image energy into a small set of low‑frequency components. High‑frequency coefficients, which contribute less to perceived quality, can be heavily quantized or discarded, achieving compression while preserving visual fidelity. This description matches option B.

Q9. What does the term 'compression ratio' represent in data compression?

A.Compressed size divided by original size

B.Original size divided by compressed size ✅

C.Ratio of bits to bytes

D.Number of bits saved per second

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Compression ratio quantifies how much a file has been reduced by dividing the original uncompressed size by the compressed size. A ratio greater than one indicates reduction, while a ratio less than one would imply expansion. Option B correctly defines this relationship.

🔗 Related Topics (MCQs)

📝 Lossless compression techniques in multimedia MCQs 📝 Lossy compression techniques in multimedia MCQs 📝 Types of multimedia data in computer networks MCQs 📝 Text representation in multimedia MCQs 📝 Image compression and formats MCQs

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