1. A method of operating a noise reduction circuit and a compression-encoding circuit, the method comprising: subtracting, in the noise reduction circuit, a value of a target pixel from a respective value of each of a plurality of pixels located in an area that includes the target pixel; for each pixel of said plurality of pixels that has a value different by at least a threshold amount from the value of the target pixel, replacing, in the noise reduction circuit, the value of said each pixel with the value of the target pixel; applying, in the noise reduction circuit, a filter function to a set of pixel values, said set of pixel values including the value of the target pixel and current values, after said replacing, of said plurality of pixels, said filter function producing a filtered video signal that is output from said noise reduction circuit; compression-encoding, in the compression-encoding circuit, the filtered video signal output from the noise reduction circuit.