Gets the reduction asked for, as a power of two: 0 (the default) for the full resolution, 1 for half, 2 for a quarter, 3 for an eighth. A codec that cannot reduce, or not that far, delivers less and says so in Reduction.
public int Reduction { get; init; }
Asked for only by a viewer drawing the image smaller than its resolution, never for printing, export or image extraction. A reduction s = 2^n of a W × H image is ⌈W / s⌉ × ⌈H / s⌉ samples, each standing for the s × s source samples it covers (see Reduction); TryCreateImage(Int32, Int32, Int32, Int32, out DecodedImageBuilder?) takes the reduced size.