JPEG XL: VarDCT block size selection
On the left, you see the selection of block types the JPEG XL encoder made. On the right, you see the decoded image.
Encoder settings are ranging from extremely high fidelity (distance 0.2) to extremely low fidelity (distance 40) – the useful range are distances 1 to 6, for higher distances the encoder is not that well-optimized yet.