The distinctiveness of the human iris has been measured by first extracting a set of features from the iris, an encoding, and then comparing these encoded feature sets to determine how distinct they are from one another. For example, John Daugman measures the distinctiveness of the human iris at 244 degrees of freedom, that is, Daugmans encoding maps irises into the equivalent of 2 ^ 244 distinct possibilities [2]. This paper shows by direct pixel-by-pixel comparison of high-quality iris images that the inherent number of degrees of freedom embodied in the human iris, independent of any encoding, is at least 536. When the resolution of these images is gradually reduced, the number of degrees of freedom decreases smoothly to 123 for the lowest resolution images tested.
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