Gets the reduction the samples were decoded at, as a power of two: 0 for the image's full resolution, 1 for half, 2 for a quarter, 3 for an eighth (Reduction).
public int Reduction { get; }
A reduction s = 2^n of a W × H image leaves Width = ⌈W / s⌉ and Height = ⌈H / s⌉ samples; sample i covers the source samples i·s to (i + 1)·s − 1, so the last one may cover less than s. Painted into the unit square (ISO 32000-2 §8.9.4), the reduced samples span ⌈W / s⌉·s / W of it, clipped at 1.