1. An image processing device comprising: a reducing section configured to generate a plurality of reduced images by reducing an input image at a plurality of reduction ratios; a noise removal processing section configured to generate noise-removed images by performing noise removal processing on each of said reduced images; an enlarging section configured to generate enlarged images equal to each other in size by enlarging each of said noise-removed images; and a mixing section configured to generate an output image by mixing two or more different enlarged images of said enlarged images with each other.