1. A method of synthesizing a synthetic image from an original real image, comprising: adding noise to the original real image to obtain a distorted image; applying an iterative optimization on the distorted image; obtaining the synthetic image based on a constraint on the distorted image subject to a fixed first quality metric and a varying second quality metric, wherein the second quality metric is a ratio of generalized means and is independent of a correlation between local regions of two or more images, and the second quality metric is defined by; R r low , r high ⁡ ( I ) ≡ ∑ r = rlow rhigh - 1 ⁢ M p r ⁡ ( I ) ( r high - r low ) ⁢ M p r high ⁡ ( I ) , ⁢ r low < r high , 1 ≤ r ≤ 4 where r=1, 2, 3, 4, a p th GM for an image vector I having elements I i is defined as: M p ⁡ ( I ) ≡ 1 N ⁡ [ ∑ i = 1 N ⁢ I i p ] 1 p wherein N is a number of elements in the image vector I and subscripts r low and r high correspond to highest and lowest values for the variable r; and outputting the synthetic image to an output device.