Gets or sets 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. A codec that honours Reduction sets it to what it delivered, which may be less than was asked for.
public int Reduction { get; set; }
A reduction s = 2^n of a W × H image leaves ⌈W / s⌉ × ⌈H / s⌉ samples (the builder's Width and Height); sample i covers the source samples i·s to (i + 1)·s − 1, the last one only those that exist.