AP CSP Day 62: Lossy vs. Lossless Compression Trade-offs | Cycle 3
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Lossless compression reduces file size without losing any information, allowing perfect reconstruction. Lossy compression permanently discards some data to achieve smaller sizes, and the original cannot be fully recovered. Choosing the wrong method can result in corrupted data or unnecessarily large files.
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Compression Methods and When Each Applies
Lossless Compression
Algorithms like ZIP, PNG, and FLAC find patterns and redundancies to shrink the file. The original data is perfectly recoverable. This is essential when every bit matters: source code, medical records, legal documents.
Lossy Compression
Algorithms like JPEG, MP3, and H.264 permanently remove information deemed less important to human perception. A decompressed JPEG is not identical to the original. Each re-compression degrades quality further.
Practice Question
A hospital stores patient medical images used by radiologists to diagnose conditions. The hospital wants to reduce storage costs. A technician proposes compressing all images using lossy compression.
Which of the following is the MOST accurate concern about this proposal?
Lossy compression permanently discards data. For medical images used in diagnosis, even small details could be clinically significant. Removing this data could lead to missed diagnoses.
A) Lossy compression can be applied to images (JPEG is the most common example). B) Compression reduces file size, not increases it. D) Processing power is not the primary concern; the irreversible data loss is the real issue.
Students focus on technical feasibility rather than the consequences of data loss. The question asks about concerns, not whether lossy compression is technically possible.
Ask: “If I decompress, do I need the EXACT original back?” If yes, lossless. If approximate is fine, lossy is acceptable.
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