Natural images from the birthplace of the human eye

Here we introduce a database of calibrated natural images publicly available through an easy-to-use web interface. Using a Nikon D70 digital SLR camera, we acquired about 5000 six-megapixel images of Okavango Delta of Botswana, a tropical savanna habitat similar to where the human eye is thought to have evolved. Some sequences of images were captured unsystematically while following a baboon troop, while others were designed to vary a single parameter such as aperture, object distance, time of day or position on the horizon. Images are available in the raw RGB format and in grayscale. Images are also available in units relevant to the physiology of human cone photoreceptors, where pixel values represent the expected number of photoisomerizations per second for cones sensitive to long (L), medium (M) and short (S) wavelengths. This database is distributed under a Creative Commons Attribution-Noncommercial Unported license to facilitate research in computer vision, psychophysics of perception, and visual neuroscience.Comment: Submitted to PLoS ON

Design of a Trichromatic Cone Array

Cones with peak sensitivity to light at long (L), medium (M) and short (S) wavelengths are unequal in number on the human retina: S cones are rare (<10%) while increasing in fraction from center to periphery, and the L/M cone proportions are highly variable between individuals. What optical properties of the eye, and statistical properties of natural scenes, might drive this organization? We found that the spatial-chromatic structure of natural scenes was largely symmetric between the L, M and S sensitivity bands. Given this symmetry, short wavelength attenuation by ocular media gave L/M cones a modest signal-to-noise advantage, which was amplified, especially in the denser central retina, by long-wavelength accommodation of the lens. Meanwhile, total information represented by the cone mosaic remained relatively insensitive to L/M proportions. Thus, the observed cone array design along with a long-wavelength accommodated lens provides a selective advantage: it is maximally informative

A unified model of illusory and occluded contour interpolation

AbstractModels of contour interpolation have been proposed for illusory contour interpolation but seldom for interpolation of occluded contours. The identity hypothesis (Kellman & Loukides, 1987; Kellman & Shipley, 1991) posits that an early interpolation mechanism is shared by interpolated contours that are ultimately perceived as either illusory or occluded. Here we propose a model of such a unified interpolation mechanism for illusory and occluded contours, building on the framework established in Heitger, von der Heydt, Peterhans, Rosenthaler, and Kubler (1998). We show that a single, neurally plausible mechanism that is consistent with the identity hypothesis also generates contour interpolations in agreement with perception for cases of transparency, self-splitting objects, interpolation with mixed boundary assignment, and “quasimodal” interpolations. Limiting cases for this local, feed-forward approach are presented, demonstrating that both early, local interpolation mechanisms and non-local scene constraints are necessary for describing the perception of interpolated contours

Forensic comparison and matching of fingerprints: using quantitative image measures for estimating error rates through understanding and predicting difficulty.

Latent fingerprint examination is a complex task that, despite advances in image processing, still fundamentally depends on the visual judgments of highly trained human examiners. Fingerprints collected from crime scenes typically contain less information than fingerprints collected under controlled conditions. Specifically, they are often noisy and distorted and may contain only a portion of the total fingerprint area. Expertise in fingerprint comparison, like other forms of perceptual expertise, such as face recognition or aircraft identification, depends on perceptual learning processes that lead to the discovery of features and relations that matter in comparing prints. Relatively little is known about the perceptual processes involved in making comparisons, and even less is known about what characteristics of fingerprint pairs make particular comparisons easy or difficult. We measured expert examiner performance and judgments of difficulty and confidence on a new fingerprint database. We developed a number of quantitative measures of image characteristics and used multiple regression techniques to discover objective predictors of error as well as perceived difficulty and confidence. A number of useful predictors emerged, and these included variables related to image quality metrics, such as intensity and contrast information, as well as measures of information quantity, such as the total fingerprint area. Also included were configural features that fingerprint experts have noted, such as the presence and clarity of global features and fingerprint ridges. Within the constraints of the overall low error rates of experts, a regression model incorporating the derived predictors demonstrated reasonable success in predicting objective difficulty for print pairs, as shown both in goodness of fit measures to the original data set and in a cross validation test. The results indicate the plausibility of using objective image metrics to predict expert performance and subjective assessment of difficulty in fingerprint comparisons

Dominance of L cones over S cones across species.

<p>Measured S cone proportion is shown for a variety of animals <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Szl1" target="_blank">[2]</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Marc1" target="_blank">[9]</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Ruderman2" target="_blank">[59]</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Wikler1" target="_blank">[82]</a>–<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Szl4" target="_blank">[90]</a>. For some animals, two measurements at different locations on the retina are shown. Large variation in L cone proportion indicates dorso-ventral asymmetries, like those discussed in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi.1000677-Szl4" target="_blank">[90]</a>.</p

Optimal mosaic after accounting for chromatic aberration.

<p>(Top) Information represented by a mixed LM array as a function of the percentage of L cones in the array is shown on the top, and similarly for an LS array (Bottom). When we model the effects of chromatic blur due to human eye optics, information transmitted by a mixed LM array was largely independent of the L/M ratio, except when one type was extremely scarce. Information transmitted by a mixed LS array was highest with ∼6% S cones.</p

Optimal mosaic using photon noise binned calculation of single cone information (see text).

<p>Results are very similar to those in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi-1000677-g005" target="_blank">Fig. 5</a>, using a Gaussian channel approximation. (Top) Information represented by a mixed LM array as a function of the percentage of L cones in the array. (Bottom) Information represented by a mixed LS array.</p

Variations in the optimal mosaic.

<p>Information per cone as a function of L cone fraction is shown for various scaling exponents, chromatic PSFs, and forms of the mutual information between cone classes. (a) Varying the scaling exponents δ<i>_L</i> and δ<i>_M</i> jointly had little affect on the flatness of the LM information curve. Differential scaling in L vs. M of about 10% led to approximately 3% higher information transmission rate for L or M dominant arrays (depending on which channel scaled with higher exponent). (b) Varying the scaling exponents, δ<i>_L</i> and δ<i>_S</i> had little affect on the optimal ratio of L and S cones, unless the L channel scaled with a substantially smaller exponent than the S channel. (c) Increasing blur in the L or M channel (while keeping the other channel's blur fixed) led to an M or L dominated optimal mosaic, respectively. A 25% increase in blur was necessary to incur a 5% advantage for a mosaic dominated (90%) by one cone class. (d) A 25% increase in the blur in the L channel relative to the S channel was necessary to significantly reduce the advantage of an L cone dominated mosaic relative to an S cone dominated mosaic. (e) Adjusting the peak or width of the form of the LM mutual information curve (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000677#pcbi-1000677-g003" target="_blank"><b>Fig. 3</b></a>) had small effects on the flatness of the LM information curve. A more peaked or narrower mutual information (see text) curve led to a 2% advantage for either an L or M dominant mosaic. A less peaked or wider mutual information curve led to a 1% advantage for an evenly mixed LM mosaic. (f) The same adjustments to the LS mutual information curve had little effect on the optimal L/S ratio.</p