The difference in the perception of the camera and the eye

Often, the image of the camera does not coincide with the picture of the surrounding world that the person filming it sees.

In this article we will describe the difference between these paintings and try to explain where it comes from. Here we will consider the features of ordinary photo and video cameras that do not have special capabilities (for example, an X-ray or a thermal imager), widely used and used by eyewitnesses to capture NOF.

What the camera sees, but the person does not see

Due to the peculiarities of camera perception, both "false NOF" and significant details explaining NOF that are not visible to the observer can appear in the images.


The first ones are collected in large numbers in the "Versions" section, so we will not talk about them in detail. Next, we will talk about what details, invisible to the observer, the camera can capture.


You can read about the features of human visual perception in a separate article on our website. Here we will touch only on some of them. 


The first feature of human vision that is worth mentioning is its selectivity. A person notices what is interesting and ignores insignificant details. Therefore, a person's perception depends on expectations, initial information, mood and other parameters. The camera, unlike a person, is impartial and can capture the whole picture, which can then be considered more thoroughly.


A person's field of vision, receptive to details, is very small – about three degrees. Peripheral vision is sensitive not to details, but primarily to movement. Therefore, in order to obtain a detailed image of the surrounding environment in the brain, the eye constantly scans it and sends information about individual fragments to the brain every moment, from which a complete picture is then formed. This principle of perception of the world, taking into account selectivity in an unusual situation, sometimes contributes to the omission of important details.


The last feature of a person's visual perception follows from the previous one – a long reaction time to an event. With a short duration of the incident, a person can perceive only a certain area of the surrounding space and skip most of the information.


All these features lead to the fact that the testimony of each of the eyewitnesses, as a rule, does not describe the full picture of the events that took place. That is why in the study of NOF (as in the investigation of any event) it's so important to interview all available witnesses. Well, photographing or videotaping an incident is of great value, since it allows you to eliminate the subjectivity of evidence and study the captured events in detail.


At the same time, the camera has a number of features that are not characteristic of the human eye:

• Perception beyond the frequency range visible to the eye. This, in particular, is explained by the sensitivity of the CCD matrix in the IR region. At the same time, black-and-white cameras, as a rule, have sensitivity orders of magnitude higher than color cameras. This feature allows you to both register objects on the camera that are not visible to a person under normal lighting (for example, the IR LED of the remote control lights up), and use it for shooting in low-light conditions (night vision cameras).

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IR LED

• The ability to adjust the exposure time. The human eye has a constant inertia of vision, and a photon of light that hits its photosensitive element has an effect that is constant and finite in duration. In the camera, you can change the duration of this action by changing the exposure time and thus forcing the photosensitive elements to accumulate information received during this time. This feature both allows you to take high-quality photos in low light, and leads to the appearance of artifacts in the pictures caused by shaking hands or objects falling into the frame, the time spent in one place is significantly less than the exposure time. Such objects can either "smear" on the image at a low speed of movement (turning into "ghosts" or "skyfish"), or not register on it at all at a high speed.

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"Skyfish"

• The presence of a flash or an additional light source when shooting. This can be both a positive factor that allows you to take high-quality pictures in low-light conditions, and a negative one that generates "false facts", for example, in the form of glare and reflections on glasses and shiny surfaces.

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Reflection on glass

• The discreteness of taking information when shooting video (the final frame rate), leading to the appearance of a stroboscopic effect in the footage.
• Internal software processing of the footage distorts the result and reduces the reliability. For example, in Galaxy S Ultra smartphones, with multiple zoom, which is necessary, including when photographing the Moon, the Scene Optimizer function is automatically activated, or "Scene Optimizer", which allows the neural network to reduce the brightness and improve the detail of the resulting photo. That is, it is not the camera that shoots in such detail, but the weak photo quality is "completed" by artificial intelligence. And it works even when shooting a table tennis ball.

What a person sees, but the camera does not see

Despite the possibility of changing the characteristics in a wide range of values, cameras remain artificial devices, and have a number of limitations compared to the human visual mechanism:

• The camera exposes the entire scene with constant, preset values of aperture, shutter speed and sensitivity, and therefore is not able to capture the difference in the degree of illumination of a high-contrast scene. The result of shooting such a scene, as a rule, is a uniformly illuminated background.

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The difference in the illumination of the scene that the human eye perceives normally

• Human vision is characterized by color variability. Our brain balances the color balance in such a way that objects retain their natural colors for us as much as possible, regardless of the color of the lighting. When shooting, a change in the color of the object's lighting inevitably leads to a change in the color of the object itself.

Conclusion

A photo or video recording of a NOF can provide additional and extremely valuable information to experts when investigating a fact. However, when analyzing them, it is necessary to take into account the features of registering the surrounding reality with a specific camera, its parameters and conditions of use.