Blur Discrimination and its Relation to Blur-Mediated Depth Perception

Abstract

Abstract. Retinal images of three-dimensional scenes often contain regions that are spatially blurred by different amounts, owing to depth variation in the scene and depth-of-focus limitations in the eye. Variations in blur between regions in the retinal image therefore offer a cue to their relative physical depths. In the first experiment we investigated apparent depth ordering in images containing two regions of random texture separated by a vertical sinusoidal border. The texture was sharp on one side of the border, and blurred on the other side. In some presentations the border itself was also blurred. Results showed that blur variation alone is sufficient to determine the apparent depth ordering. A subsequent series of experiments measured blur-discrimination thresholds with stimuli similar to those used in the depth-ordering experiment. Weber fractions for blur discrimination ranged from 0.28 to 0.56. It is concluded that the utility of blur variation as a depth cue is constrained by the relatively mediocre ability of observers to discriminate different levels of blur. Blur is best viewed as a relatively coarse, qualitative depth cue.

Human Discrimination of Depth of Field in Stereoscopic and Nonstereoscopic Photographs

“…The results showed that the increment threshold of blur first decreased and then increased with increasing levels of blur in the reference blur circle, resulting in a parabolic shape of the relationship between the threshold and the reference blur with a peak sensitivity around one arcmin. Consistency in these results was shown across a variety of studies in spite of different stimuli and experimental methods (Hess, Pointer, & Watt, 1989;Mather, 1997;Mather & Smith, 2002;Watt & Morgan, 1983;Wuerger, Owens, & Westland, 2001). Assuming a peak ability to discriminate blur at about one arcmin, we may predict that this value is the limiting factor in discriminating DOF.…”

“…First, the definition of DOF in our paper was based on the blur circle of one arcmin. Second, the peak sensitivity for blur discrimination was found to be around one arcmin (Chen, Chen, Tseng, Kuo, & Wu, 2009;Hamerly & Dvorak, 1981;Hess, Pointer, Simmers, & Bex, 2003;Mather & Smith, 2002;Watt & Morgan, 1983).…”

“…DOF is generated in photographs as a result of optics of the imaging equipment, most often manipulated by varying the aperture size of the camera. In addition, most previous studies on blur discrimination used single blurred edges (Georgeson, 1998;Hamerly & Dvorak, 1981;Pääkkönen & Morgan, 1994), binary texture (Hoffman & Banks, 2010), or random dot stereograms (Mather & Smith, 2002), rendered by computer algorithms. In contrast, our stimuli contained a blur gradient over the figures in the scene that was affected by the scale of the scene.…”

“…For example, Hamerly and Dvorak (1981) investigated edge and line blur discrimination and found that observers could discriminate a blurred from a sharp high-contrast photograph when the edgetransition width was above 25 arcsec. Mather and Smith (2002) conducted an experiment to investigate blur discrimination of three kinds of blur: luminance border, texture border, and region blur. The results showed that the increment threshold of blur first decreased and then increased with increasing levels of blur in the reference blur circle, resulting in a parabolic shape of the relationship between the threshold and the reference blur with a peak sensitivity around one arcmin.…”

A luminance-contrast-aware disparity model and applications

“…Mather et al [2002] showed that when only pictorial cues are considered, the blurred textures in Fig. 2 should appear as being behind the others.…”