1. A noise eliminator, comprising: a noise distribution analysis section which analyzes a first image signal acquired by an imaging device with light blocked to determine the magnitude distribution of the first image signal of some or all pixels constituting the imaging device, specifies from this distribution a range within which a peak magnitude of the first image signal is included, and defines a threshold value within this range; a quantization section which quantizes, based on the threshold value, a second image signal acquired by the imaging device with light blocked; an inverse quantization section which inversely quantizes the quantized second image signal; and a subtraction section which subtracts the inversely quantized second image signal from a third image signal acquired by the imaging device with light incident thereon.