Compression Ratio
The ratio between original and compressed data sizes. Higher ratios yield smaller files but may introduce quality loss in lossy formats.
Compression ratio expresses the relationship between original and compressed data sizes. A 10 MB image compressed to 1 MB achieves a 10:1 ratio (90% reduction). For web delivery, file size directly impacts loading speed, making compression ratio selection critical.
In lossy compression formats like JPEG, the quality parameter (1-100) controls the ratio. Quality 80 is a commonly used starting point for balancing visual fidelity against size reduction, and block artifacts become easier to notice as the value is lowered. Lossless formats like PNG achieve ratios dependent on image content, with flat-color regions compressing more efficiently.
The image compression tool provides a quality slider for real-time ratio adjustment with preview. Modern formats like WebP and AVIF often yield smaller files than JPEG at equivalent visual quality, though the margin varies with image content and settings.