Why Compressing an Image to Exactly 50KB Is Harder Than It Sounds

Short summary

An in-depth explanation of why compressing an image to an exact target file size is a non-trivial optimization problem. JPEG quality controls quantization tables, not file size directly, and the relationship varies wildly by image content and is non-linear. A robust compressor must search across quality, dimensions, chroma subsampling, and format together rather than tuning quality alone.

• •JPEG quality controls quantization aggressiveness, not file size — same quality produces 5-10x size differences across images
• •Quality-to-size curve is non-linear and flattens at low quality, making naive binary search inefficient near the floor
• •Robust compression requires searching quality, dimensions, chroma subsampling, and format together

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