Gets or sets the fewest decoded samples per device pixel a reduced image keeps when ScaledImageDecode is on: DefaultImageSamplesPerPixel (2) by default. 1 decodes less and renders faster, at a coarser average (35 to 48 dB against a full decode on photographs, where 2 gives 36 to 54 dB).
public double ImageSamplesPerPixel { get; set; }
ISO 32000-2 §8.9.4: the count is taken along the image's most enlarged direction in device space, so rotation and skew never leave fewer.