Human discrimination of fractal images

David C. Knill, David Field, Daniel Kerstent

Research output: Contribution to journalArticlepeer-review

135 Scopus citations


In order to transmit information in images efficiently, the visual system should be tuned to the statistical structure of the ensemble of images that it sees. Several authors have suggested that the ensemble of natural images exhibits fractal behavior and, therefore, has a power spectrum that drops off proportionally to l/fB(2 <β<4). In this paper we investigate the question of which value of the exponent describes the power spectrum of the ensemble of images to which the visual system is optimally tuned. An experiment in which subjects were asked to discriminate randomly generated noise textures based on their spectral drop-off was used. Whereas the discrimination-threshold function of an ideal observer was flat for different spectral drop-offs, human observers showed a broad peak in sensitivity for 2.8 < β < 3.6. The results are consistent with, but do not provide direct evidence for, the theory that the visual system is tuned to an ensemble of images with Markov statistics.

Original languageEnglish (US)
Pages (from-to)1113-1123
Number of pages11
JournalJournal of the Optical Society of America A: Optics and Image Science, and Vision
Issue number6
StatePublished - Jun 1990

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