The Utility of Defocus Blur in Binocular Depth Perception

Dhanraj Vishwanath

doi:10.1068/i0544ic

Abstract

The question of whether defocus blur is a quantitative cue for depth perception is a topic of renewed interest. A recent study suggests that relative defocus blur can be used in computing depth throughout the visual field, particularly in regions where disparity loses precision. However, elements of the study's experimental design and theoretical analysis appear to undermine this claim. First, the study did not provide evidence that blur can be used as a quantitative depth cue. It only measured blur discrimination thresholds, not perceived depth from for blur. Second, the study's conceptualization of the complementary use of blur and disparity, and related conjectures, are based on the specific viewing geometry and fixation distance tested. They do not appear to generalize to natural viewing situations and tasks. I suggest a different way in which defocus blur might affect depth perception. Because depth-of-focus blur is a cue to egocentric distance, it could contribute to quantitative depth perception by scaling depth relations specified by other relative depth cues.

Highlights

They claim that disparity is used to compute z1 – z0 when it has a small value, whereas defocus blur is used when it has a large value
Held et al never tested if quantitative depth separation z1 – z0 can be estimated from blur
Held et al.’s conjectures regarding the use of blur for precision depth judgments and motor tasks are based on an artificial binocular task geometry (Figures 1a and b) and fixation distance (28 cm) that create large absolute disparities and diplopia for the farther object

Summary

Introduction

They claim that disparity is used to compute z1 – z0 when it has a small value, whereas defocus blur is used when it has a large value. Their task measured discrimination thresholds for judging the ordinal depth between two objects beyond fixation (i.e., z2 > z1; see Figure 1b).

Results

Conclusion