STEM与日常科技·英语30篇（3）
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JPEG Compression Artifacts and Block-Based Encoding Limitations
JPEG压缩伪影与基于分块编码的固有局限
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JPEG divides images into 8×8 pixel blocks before applying discrete cosine transform and quantization.
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High compression ratios force aggressive quantization, discarding fine frequency details from each block.
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When reconstructed, these simplified blocks often show visible edges where their colors or brightness differ slightly.
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These square-shaped distortions are called blocking artifacts—and worsen near sharp transitions like text or hair.
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JPEG cannot smooth boundaries between blocks because it processes them independently without overlap.
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Low-light photos or heavily compressed web thumbnails reveal these artifacts most clearly under magnification.
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Modern formats like WebP and AVIF reduce blocking by using larger transforms or adaptive block sizes.
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Still, JPEG remains widely used because its trade-off between size and quality suits everyday sharing well.
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Understanding blocking helps photographers choose optimal settings before uploading high-detail images.
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It also reminds us that all lossy compression sacrifices some truth for practical convenience.