Quality factor
Definition
The 1-100 scale that most JPEG encoders expose to the user, controlling how aggressively the quantisation table rounds coefficients. The factor is usually stored in the file header alongside the table itself.
Related terms
- Blocking artefacts
- Visible rectangular discontinuities at 8x8 block boundaries, caused by independent quantisation of adjacent blocks. At splice boundaries, misaligned block grids produce a...
- DCT (Discrete Cosine Transform)
- The mathematical transformation applied to each 8x8 pixel block during JPEG compression, converting spatial pixel values into a set of frequency coefficients...
- Double-JPEG compression
- The result of decoding a JPEG, applying any edit, and saving as JPEG again. The coefficient histograms of doubly-compressed images have a...
- JPEG ghost
- A localisation method that re-saves the image at multiple quality levels, then maps per-pixel residuals to find regions whose minimum error quality...
- Quantisation table
- A matrix of divisors applied to DCT coefficients during JPEG compression. Higher divisors produce lower quality. The specific table used is often...
Explained in
- JPEG Compression Artefacts and Double-Compression DetectionThe 1-100 scale that most JPEG encoders expose to the user, controlling how aggressively the quantisation table rounds coefficients. The factor is usually stor...