1. An image processor configured to perform denoising on an input image to generate an output image, the image processor comprising: a transform circuit configured to transform first image data of a spatial region extracted from the input image in a unit of a predetermined block into second image data of a frequency region including a plurality of frequency components; a quantization circuit configured to perform quantization on the second image data to generate third image data; a first arithmetic circuit configured to calculate a per-block noise value based on the first image data; and a first quantization value setting circuit configured to set a first quantization value per input image for quantization based on a noise value of the whole input image.