1. An image processor configured to perform denoising on an input image to generate an outputa 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 first arithmetic circuit configured to calculate a per-block noise value based on the first image data: a first quantization value setting circuit configured to set a first quantization value per input image based on a noise value of the whole input image; a quantization circuit configured to quantize the second image data based on the first quantization value to generate third image data with noise in the input image removed; and an output circuit configured to generate the output image based on the third image data.