Uncovering the hidden distortions in body-worn camera footage

One of our roles at Critical Incident Review is to develop an understanding of video evidence related to the review and analysis of police use-of-force incidents.

One of the paramount issues is the distortion of the appearance of distance in the video evidence. This can be extreme, as demonstrated in this project.

We utilized a 50mm lens and an Axon 4 body-worn camera to show an approximation of the gross distance distortions represented in the video evidence produced by these cameras.

You will quickly notice that distance is significantly misrepresented on the body-worn camera. These cameras are designed to capture a wider breadth of visual information, so the fisheye lens distorts the appearance of vastness at peak lens distance. These distortions in the body-worn camera evidence can give the appearance that the officer was much further from the threat than the officer was in reality. This distortion can then affect the appearance of time, the appearance of speed, and the appearance of motion. It can even affect when the individual was perceived to become a threat, or if the reviewer believes that the subject was a threat to begin with.

The what

We conducted a comparison between a 50mm lens representing the human eye and an Axon 4 body-worn camera with a fisheye lens. Here’s what this comparison reveals:

Perspective and field of view: The 50mm lens approximates the field of view of the human eye, providing a familiar perspective and angle of view. Comparing it with the fisheye lens on the Axon 4 body-worn camera allows for an understanding of how different lenses capture and represent the surrounding environment. This comparison helps evaluate the distortion introduced by fisheye lenses, which can be crucial for accurate scene documentation and analysis.

Accuracy in documentation: In fields such as law enforcement and accident reconstruction, accurate documentation of scenes is essential for investigations, evidence collection and legal proceedings. Understanding the differences between the perspective captured by a 50mm lens and a fisheye lens helps ensure that recorded footage accurately represents the spatial relationships and distances within the scene.

Visual representation: Different lenses produce distinct visual representations of scenes. This can influence how individuals perceive and interpret the recorded footage. Comparing footage captured with a 50mm lens and a fisheye lens allows for an assessment of visual accuracy, distortion, and realism. This comparison helps determine which lens type provides the most accurate and informative representation of the scene.

In this series of pictures, the officer is holding a 15-inch spatula.

The 50mm picture on the top shows the officer at 12ft from the camera lens. In the image below, we added white reference lines depicting the curvature in the lenses.

Photos/Critical Incident Review

The 50mm picture below shows the officer at 22ft from the camera lens.

Photo/Critical Incident Review

Impact on perception: Fisheye lenses introduce significant distortion, exaggerating the size and curvature of objects at the edges of the frame. This distortion can affect the perception and judgment of those conducting the analysis, potentially leading to inaccuracies in distance estimation, object size and spatial relationships. By comparing footage captured with different lenses, those investigating, reviewing and analyzing can better understand the impact of lens distortion on perception and cognitive processes.

Training and education: Comparing different lenses enhances training and education in fields where scene documentation is crucial, such as law enforcement, emergency response and accident investigation. By understanding the strengths and limitations of different lenses, practitioners can make informed decisions about equipment selection (camera), scene documentation techniques, and analysis methodologies.

Photo/Critical Incident Review

Photo/Critical Incident Review

Standardization and best practices: Establishing standards and best practices for scene documentation and analysis requires a thorough understanding of the capabilities and limitations of available camera equipment, including camera lenses. Comparative studies between a 50mm lens and a fisheye lens (your agency’s BWC) contribute to the development of guidelines and protocols for accurate and reliable documentation in various fields.

Comparing a 50mm lens representing the human eye with an Axon body-worn camera with a fisheye lens is essential for understanding the differences in perspective, distortion and visual representation. This comparison informs scene documentation, perception issues, training programs, and the establishment of standards and best practices in fields where accurate visual documentation is paramount.

A 50mm lens is often considered to closely replicate the field of view of the human eye on a full-frame camera. Here’s why:

Angle of view: A 50mm lens on a full-frame camera typically provides a horizontal angle of view of around 40-45 degrees, which closely matches the human eye’s natural field of view. This means that when you look through a camera with a 50mm lens, the scene you see will be similar to what you would perceive with your own eyes in terms of the width of the scene. (We used a crop sensor camera, not a full frame in this demonstration).

Perspective: The perspective rendered by a 50mm lens is relatively natural and similar to what the human eye sees. Objects in the frame appear with proportions that are familiar to us, without any significant distortion or exaggeration.

In the image below, the subject is running at the camera position and is approximately 14-15 feet away from it. On the left, the suspect is holding a 6-inch knife. On the right, the subject is holding a remote-control clicker.

Photo/Critical Incident Review

Now, let’s contrast this with other types of lenses:

• Body-worn camera: These cameras often have wide-angle lenses, which capture a much broader field of view than the human eye. While they are great for capturing a wide scene or for surveillance purposes, they tend to distort perspective, making objects at the edges of the frame appear stretched or elongated.
• Fisheye lenses: Fisheye lenses have an extremely wide field of view, often exceeding 180 degrees. They create a characteristic distortion effect, where straight lines appear curved, giving a surreal or exaggerated perspective. While fisheye lenses can be creatively used for artistic purposes or to capture immersive scenes, they do not provide a representation of reality that closely matches the human eye’s perception.

While a 50mm lens on a full-frame camera closely approximates the perspective and field of view of the human eye, body-worn cameras and fisheye lenses offer different visual effects that can be creatively used to gather and record a wider breadth of visual information but don’t replicate the natural human perception as closely.

Visual range: This is the available visual data out to approximately 210 degrees for the human eye — visual range is all of the visual data available to us from our focal vision or foveal vision out to our extreme peripheral vision. This could also be considered our visual field, however, visual acuity within the visual field is approximately 1 to 3° of our entire visual field.

The visual range, or the visual field of a camera lens is the entire range of recorded data within the camera’s view. In the below example we have outlined the areas within the visual field to include focal vision or foveal vision, parafoveal vision, near peripheral vision, and peripheral vision out to approximately 180°-190°.

Photo/Critical Incident Review

The distortion between a body-worn camera and a standard 50mm lens (or human eye) in terms of distance perception can vary significantly depending on factors such as the specific lens used, the distance between the camera and the subject, and the angle of view.

A body-worn camera with a wide-angle lens can introduce significant distortion, making some objects appear closer than they actually are. This distortion is due to the lens’s wide field of view, which captures a larger area but compresses the perspective, making objects at the edges of the frame appear closer to the center.

In contrast, a standard 50mm lens on a full-frame camera provides a more natural perspective, closely approximating what the human eye sees. A 50 mm lens typically causes less distortion of distance perception than a wide-angle lens.

It’s challenging to provide an exact percentage of distortion without specific parameters, but in general, the distortion introduced by a wide-angle lens can make objects appear closer by several feet or meters, depending on the distance from the camera and the focal length of the lens. This distortion can potentially impact the assessment of distances in an officer-involved event and needs to be considered when analyzing footage or eyewitness testimony.

Resolution of the eye v. the camera

Comparing the human eye to a camera lens in terms of megapixels involves understanding the resolution capabilities of both systems. Here’s how you can approach this comparison:

Human eye resolution

• The human eye does not have a fixed resolution in the same way that a camera does. Instead, its resolution is often described in terms of visual acuity, which refers to the ability to discern fine details.
• The human eye has an estimated resolution equivalent to around 576 megapixels (MP) when considering the entire field of view. This estimate is based on the density of photoreceptor cells on the retina and the brain’s processing capabilities.

Camera lens resolution

• Camera resolution is typically measured in megapixels, which represent the number of individual pixels captured in an image.
• The resolution of a camera lens depends on factors such as the sensor size, pixel count, and optical quality of the lens. Higher megapixel counts generally result in sharper and more detailed images.
• For example, a camera with a 24-megapixel sensor captures images with a resolution of approximately 6000 x 4000 pixels.

Comparison and limitations

• While the human eye has a theoretical resolution equivalent to hundreds of megapixels, it’s essential to note that this estimate does not directly translate to the resolution of a camera sensor.
• Camera sensors may have higher megapixel counts than the human eye’s estimated resolution, but they may not always produce images with the same level of detail and clarity. Factors such as lens quality, sensor size, and image processing algorithms also influence image quality.
• Additionally, the human eye’s ability to perceive detail is not solely determined by resolution. Factors such as contrast sensitivity, dynamic range, and color perception also contribute to our overall visual experience.

Practical considerations

• While cameras with high-resolution sensors can capture fine details, they may not always replicate the human eye’s perception faithfully. The human eye’s dynamic range, ability to adapt to changing lighting conditions, and three-dimensional perception contribute to a richer visual experience that cameras cannot fully replicate.
• However, high-resolution cameras are valuable tools for tasks such as scientific imaging, documentation, and forensic analysis, where capturing fine details is essential.

Comparing the human eye to a camera lens in terms of megapixels provides insight into the resolution capabilities of both systems. While the human eye has an estimated resolution equivalent to hundreds of megapixels, camera sensors may have higher megapixel counts but may not always replicate the human eye’s perception accurately. Understanding the differences and limitations of each system is essential for effective visual documentation and analysis.

How

Performing a comparison between a 50mm lens representing the human eye and a body-worn camera with a specialized lens specification in an officer-involved critical incident involves a structured approach to understanding the differences in perspective, distortion, and visual representation. Recently CIR was involved in a scene recreation whereby the comparison of the actual body-worn camera of the officer involved was used to recreate and compare the incident with the use of a 50mm lens for all the reasons identified above. Here’s a detailed description of how you can conduct this comparison effectively:

Select comparable scenarios

If the comparison demonstration is specific to a case, you must use the scene location of the event for the demonstration. If it is a general demonstrative, identify specific scenarios or environments relevant to the critical incident where accurate documentation and perception are essential. Choose locations with varying distances, lighting conditions, and spatial complexity to capture a range of visual challenges.

Setup and equipment preparation

• Set up both the 50mm lens camera and the body-worn camera in fixed positions or on stable mounts to ensure consistent framing.
• If necessary, verify that both cameras are recording at the same resolution and frame rate for fair comparison. (depending on the purpose of the comparison)
• These lens need to be as close in relation to one another as possible.
• This hypothetical also doesn’t address the distance/variability between the eyeline and the bodyworn position of the camera.
• Capture the S/N and specifications of the body camera and the specifications of the camera and lens you are using.

Capture test footage

• Record test footage using both cameras simultaneously in each selected scenario. Ensure that both cameras capture the same scene from their respective perspectives.
• Instruct the officer (or actor) to move within the scene to simulate different viewing angles and distances relevant to the critical incident.

Review and analysis

• Playback the recorded footage from both cameras side by side to compare their visual representations. Pay attention to differences in perspective, distortion, and spatial relationships.
• Measure all aspects of the recreation, including lens height from the ground on both lenses being utilized in the comparison, the distance from the center of each lens in association with each other, and any distances that change during the recreation and capture of the incident. In addition once the scene has been recreated, measure the distance between the actors (officer and subject).
• Evaluate the extent of distortion introduced by the fisheye lens in the body-worn camera footage. Note any discrepancies in object size, shape, and curvature compared to the 50mm lens footage.
• Assess the accuracy of distance estimation and spatial awareness in both sets of footage. Determine whether the fisheye lens distorts distance perception and impacts situational awareness.
• if necessary, have the ability and the means to go through the original video from the incident frame by frame. This allows the investigator to identify decision points, or potential decision points during the incident. This will be based on statements from officers, witness statements, and other physical and forensic evidence collected during the original event.

Documentation and reporting

• Document your observations, findings, and conclusions from the comparison process. Include detailed descriptions of the visual differences between the 50mm lens and fisheye lens footage. Measurements and deliberate tracking of the process is imperative.

Training and awareness

• Use the comparison results to enhance officer training and awareness regarding the limitations of fisheye lenses in body-worn cameras. Emphasize the importance of critical thinking and context awareness in interpreting visual information during high-stress situations.
• Incorporate the comparison findings into ongoing training programs and debriefings to foster a deeper understanding of the role of perception and visual representation in officer-involved critical incidents. This will serve an important purpose regarding an officer watching a video prior to, or subsequent to, a statement or a report. The more these distortions are discovered and shared regarding these critical incidents, the more officers will understand What can potentially misrepresent their own experience in reality in the critical incident.

Photo/Critical Incident Review

By following this structured approach to comparison and analysis, you can gain valuable insights into the differences between a 50mm lens representing the human eye and a body-worn camera with a fisheye lens. This understanding contributes to improved scene documentation, perception awareness, and decision-making in officer-involved critical incidents.

In this demonstrative, we marked measurements and captured digital representations of multiple distances with the camera lenses aligned at the same distance and height. Additionally, cell phone video is included in the comparison so that there is a full understanding of perspective issues based on the complexities of digital video encoding, lens specification, and other potential variables that can affect what the digital video represents to the reviewer, as the “reality” that the officer experienced at the moment. We discuss the variables in time, distance, speed, and motion and how these components can be distorted both in the encoding of digital video and in the memory of an individual experiencing a critical event under the constraints of time and possibly facing the consequences of life and death can have a vehement effect on the analysis of the incident whereby video evidence is being heavily relied upon. To learn more about the review and examination technicalities regarding an officer-involved critical incident please visit criticalincidentreview.com and explore our upcoming Enhanced Force Investigation courses, and our Force Analysis, Forensic Video Review and Examination course.

This demonstration

Photo/Critical Incident Review

The main difference between the human eye and a camera lens lies in their mechanisms of capturing and processing visual information:

Biological vs. mechanical: The human eye is a biological organ that captures and processes light through a complex system of structures, including the cornea, lens, retina, and optic nerve. In contrast, a camera lens is a mechanical device that uses glass elements to focus light onto a sensor or film.

Adaptability: The human eye is highly adaptable, capable of adjusting its focus, aperture (pupil size), and sensitivity to light in real-time to accommodate changes in lighting conditions and viewing distances. Camera lenses, while offering various focal lengths and apertures, lack the dynamic adaptability of the human eye.

Processing: Visual information captured by the human eye is processed by the brain’s visual cortex, where it undergoes complex interpretation, pattern recognition, and integration with other sensory inputs. In contrast, a camera captures images as digital or analog data, which can be further processed using software or editing techniques but lacks the cognitive interpretation capabilities of the human brain.

Field of view and resolution: The human eye has a wide field of view and high resolution, providing perception across a broad visual field but only a small area, 1-3 degrees of visual angle of visual acuity. Camera lenses vary in their field of view and resolution capabilities, depending on factors such as focal length, sensor size, and lens quality.

While both the human eye and camera lens serve the purpose of capturing visual information, they operate through fundamentally different mechanisms and have distinct advantages and limitations.

Another primary difference between the eye and the camera lens is simply the fact that the camera is not attached to a human brain. The interpretive process of the brain plays a crucial role in shaping our perception of the world around us. Here’s a brief explanation of how this process works and its significance to what the camera records and what the brain “sees”:

Selective attention: The brain receives a vast amount of sensory information from the environment through the eyes. However, it cannot process all this information simultaneously. Instead, the brain employs selective attention mechanisms to filter out irrelevant stimuli and focus on what is deemed important or salient. This allows us to prioritize certain aspects of our visual environment while ignoring others.

Perceptual organization: Once sensory information has been filtered, the brain organizes it into meaningful patterns and structures. This process, known as perceptual organization, involves grouping visual elements based on principles such as proximity, similarity, continuity, and closure. By organizing sensory input into coherent perceptual units, the brain makes sense of the visual scene and extracts relevant information.

Interpretation and meaning: The brain’s interpretation of visual stimuli is heavily influenced by prior knowledge, experience, and expectations. For example, when viewing a familiar object, such as a chair, the brain quickly identifies it based on stored representations of chairs and attributes meaning to it (e.g., something to sit on). Similarly, cultural factors and learned associations influence how we interpret visual cues and assign meaning to them.

Visual illusions and biases: The interpretive process of the brain can sometimes lead to perceptual errors, such as visual illusions and biases. Illusions occur when the brain misinterprets visual stimuli, leading to discrepancies between perception and reality. Biases, on the other hand, arise from preconceived beliefs or expectations that influence how we perceive and interpret visual information. These phenomena demonstrate the brain’s tendency to impose its own interpretations on incoming sensory data, sometimes deviating from objective reality.

Context and integration: The brain integrates visual information with other sensory modalities and cognitive processes to form a coherent perception of the environment. Contextual cues, such as background information and situational factors, help guide the interpretation of visual stimuli and provide additional meaning to the perceived scene. Integration across different sensory channels allows for a more robust and comprehensive understanding of the world.

Adaptation and plasticity: The interpretive process of the brain is dynamic and adaptive, allowing for flexibility in response to changing environmental conditions. Through processes such as neural plasticity, the brain can modify its interpretation of visual stimuli based on learning and experience. This adaptability enables us to adjust to new situations and environments, continually refining our perception over time.

The interpretive process of the brain plays a fundamental role in shaping our perception of the visual world; this is not the role of the camera lens and the storage of digital visual data. By selectively attending to relevant stimuli, organizing sensory input into meaningful patterns, and integrating contextual information, the brain constructs a rich and nuanced representation of our surroundings. However, this interpretation is subjective and can be influenced by factors such as attention, prior knowledge, and cultural background, highlighting the complex interplay between sensory input and cognitive processing in visual perception. When the visual distortions that are associated with the encoding of digital video information, primarily the distortion of distance, which can also affect the appearance of movement and speed, which ultimately can affect how quickly or how slowly things appear to be happening in the encoded video setting. An encoded video is simply a digital representation (of the officers environment, not…) of an officer’s reality, which is experienced, not recorded.

Here’s a brief explanation of the differences between a video camera and the human eye, as well as how perception and interpretation play a crucial role in vision:

Mechanism of capture

• Video camera: A video camera captures images using a sensor (such as a CCD or CMOS sensor) that converts light into electronic signals. These signals are then processed and stored as digital data.
• Human eye: The human eye captures images through a complex biological process. Light enters through the cornea and passes through the pupil, which regulates the amount of light. The lens focuses the light onto the retina, where photoreceptor cells (rods and cones) convert light into electrical signals. These signals are then transmitted through the optic nerve to the brain for processing.

Image processing

• Video camera: The electronic signals captured by the sensor are processed by the camera’s image processing circuitry. This processing may involve adjustments to exposure, white balance, contrast, and color, among other factors.
• Human eye: The visual information captured by the retina is processed by the brain’s visual cortex. This processing involves various stages, including edge detection, motion detection, depth perception, and object recognition. The brain integrates this information to construct a coherent and meaningful visual perception.

Field of view and resolution

• Video camera: The field of view and resolution of a video camera are determined by its lens and sensor. Different lenses can provide varying angles of view, and sensors with higher pixel counts can capture more detail.
• Human eye: The human eye has a wide field of view and high resolution, allowing for detailed perception across a broad visual field. Moreover, the eye can rapidly adjust its focus and perceive a wide range of brightness levels.

Perception and interpretation

• Video camera: A video camera captures visual information objectively, without interpretation or filtering. However, the interpretation of the recorded footage may vary depending on factors such as context, observer bias, and cultural influences.
• Human eye: Vision is not solely determined by the input received by the eye but also by the brain’s interpretation and processing of that information. The brain filters and interprets visual stimuli based on factors such as attention, expectation, memory, and emotional state. This selective processing helps focus attention on relevant information while filtering out distractions.

While both video cameras and the human eye capture visual information, they operate through fundamentally different mechanisms. The human eye’s perception is not only influenced by the raw sensory input but also by complex cognitive processes that shape our interpretation of the visual world.

References

Daigle A. (May 13, 2018.) How the 50-mm Lens Became ‘Normal.’ The Atlantic.

Green M. (2008.) Forensic Vision. Tucson AZ: Lawyers and Judges Publishing Co.

Green M. (2021.) visualexpert.com.

Cash S. (2023.) Video Analysis in Collision Reconstruction. Covenant Garden: Independent Publishing Network.

Demonstrative prepared, authored and produced by Jamie Borden, Critical Incident Review, L.L.C. (CIR) www.CriticalIncidentReview.com, and Danny King, www.AmericanPatrolman.com. All rights reserved.