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"Is the Camera the Same as the Human Eye?" - A Visibility Expert Discusses the Complexity of Using Video Photography to Inform and Persuade Jurors

By: Paul Kayfetz
Tel: 415-868-0480
Email Mr. Kayfetz


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Q: "Is the camera the same as the human eye?"

A: "No." This is as frequently asserted as a "gotcha" question during cross examination attacking a driver's eye visibility study.

Q: "Then the visibility study does not show what the driver could have seen!"

A: "That is not correct; the jurors have eyes."

The explanation then given is a basic, but little understood, fundamental of the presentation of a visibility study in court.

A visibility study depicts what is available to be seen by a person with normal, unimpaired vision under defined conditions similar enough to those at issue to provide relevant information about levels of visibility, lines-of-sight, timing of visibility, and to demonstrate expert witness(es)' opinions.

The content of a visibility study is an image of the subject scene, which may be from the driver's position looking through the windshield, the bicyclist glancing back over his shoulder - or whatever is relevant.

The crucial factor is that the camera, video, and processing are all just means to an end. That end is bringing into the courtroom, on a screen before the jury, an image of the real world which was in front of the driver/bicyclist/whomever when the subject incident occurred.

Each juror's eyes close the loop. This is where "the human eye" becomes a part of the visibility study process. Each juror looks at an image which is as close to life size as necessary for the issues of the particular case. This image includes the entire windshield A-pillar to A-pillar, the dashboard instruments, and the view out the side windows if relevant.

The complexity of human vision now comes back into play: The juror looking at the image on the screen sees a small central foveal area in his field of view most sharply; the edges of his visual image are increasingly fuzzy out toward peripheral vision; but, his eyes scan areato- area subconsciously so quickly that the entire image seems in focus. The juror's "human eye" has now become the final part of the visibility study.

Closing the loop for jurors

Essential to allowing the jurors' eyes close the loop is putting enough of the scene into the courtroom that relevant aspects are not trimmed out.

A driver's eye view provides the most common example. In automobile situations a minimum image - to replicate areas scanned by a driver - must include the entire windshield, the speedometer, other gauges, and the center rearview mirror. In some incidents, side window and mirrors must be included. This image width and height cannot be obtained from a driver's head position with typical consumer or prosumer video cameras; these normally have only a 40 degree angle of view. Professional HD or 4K cameras with a minimum 90 degree horizontal angle of view are required. (The only exceptions are the GoPro [and similar] sports cameras. These, however, do not allow sufficient manual exposure control to handle nighttime road scenes nor daytime scenes going in and out of shadows.)

If side windows and mirrors must be included, two or three professional cameras are mounted pointed at different angles in the head position and the several images spliced together during computer editor processing.

Specialized projection equipment is needed in court. A 7000 lumen projector - two to three times brighter than those typically available through courtroom services - provides enough brightness to override courtroom security lighting or window ambient illumination. This is particularly necessary when showing nighttime visibility studies.

In order to afford the jury as close to a life-size image as possible, a large screen is positioned close to them. A specialized 90 degree wide field lens allows an 8 foot-wide screen to be placed 8 feet from the jury box, yet with the projector below the jurors' line-of-sight.

Precise juror viewing distance from the screen is only critical if the limiting factor in hazard visibility and recognition is size, conspicuity (contrast against background), or subject angle-off-axis. In some cases where one of these factors was significant, judges have allowed pairs of jurors at-a-time to view the visibility study, one seated on each side of the projector lens, with the screen facing away from the jury box. Rotating the viewing through the jury in this manner usually takes less time than the arguments about whether to undertake the procedure.

Foundation and the concept of expectancy

. . .Continue to read rest of article (PDF).


Paul Kayfetz prepares HD-video visibility studies and provides foundation expert testimony to get them into evidence, and to explain the results of the studies. He has testified as an expert witness in Engineering Photography more than 500 times across the country. In addition, he is the author, and co-author with Human Factors Experts, of five nationallypublished technical papers on these topics. Attorneys retain him for consultation to keep opposing animations/simulations/visibility studies out of evidence - or to use judo to turn them against their promulgator. He also enhances hidden detail from video, and makes measurements from existing photos or video.

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