1. A method of producing a visibility metric from a digital reference image and a digital test image, the method comprising: a) producing a reference luminance image from the reference image and a test luminance image from the test image; b) producing a local mean luminance reference image as a convolution of the reference luminance image and a luminance filter function; c) producing a test contrast image as at least one of the following: (c1) a mathematical combination of the test luminance image and the local mean luminance reference image and (c2) a mathematical combination of the test luminance image, the local mean luminance reference image and a border aperture function and (c3) a mathematical combination of the test luminance image, the local mean luminance reference image and an image of a border surrounding the reference image; d) producing a reference contrast image as at least one of the following: (d1) a mathematical combination of the reference luminance image and the local mean luminance reference image and (d2) a mathematical combination of the reference luminance image, the local mean luminance reference image and the border aperture function; e) applying a contrast sensitivity filter to the test contrast image to produce a filtered test image; f) applying the contrast sensitivity filter to the reference contrast image to produce a filtered reference image; g) providing a difference image by at least one of the following two processes: (g1) subtracting the filtered reference image from the filtered test image to produce a difference image, and (g2) producing a mask image as a mathematical combination of the filtered reference image with a masking filter, and producing a difference image as a ratio of the difference image and the mask image; h) producing a just noticeable difference image as a mathematical combination of the difference image with a window function; and i) pooling the just noticeable difference image to produce a visibility metric.