Minimum illumination for video monitoring cameras choosing correctly

Due to lack of standards, rules and freedom in the specification of products by manufacturers, integrators and end users find some difficulty choosing the best camera for video monitoring for a particular application, or even compare models from different brands.

Introduction

Due to lack of standards, rules and freedom in the specification of products by manufacturers, integrators and end users find some difficulty choosing the best camera for video monitoring for a particular application, or even compare models from different brands.

Figure 1: Information provided by manufacturers.

The minimum illumination

Minimum illumination reported in the technical specification of a camera, derived from tests performed by the manufacturer, and indicates the way in which the sensitivity of the camera is measured. In other words, it is a value indicating the minimum amount of light (lux) required to represent a usable image, that is, which can identify persons and / or objects.

The "usable image" is not equal to the "original image", ie, the brightness and contrast are always lower, therefore, the manufacturer must indicate what level of signal amplitude (IRE) obtained from tests product.

From these tests other measurements must be reported, as the F-Stop lens, the colour temperature of the light used, and the reflection of the object in the lens (F-Stop) and light (temperature are also obtained color). These parameters will explain below:

Signal level - IRE

Unit of measure of the level of video signal. The maximum amplitude of the video is 100 IRE, which would have a camera to show a picture with enhanced brightness and contrast possible. An example is when a camera is monitoring a crude white wall, an image with enough to represent a signal of the 100 IRE would show on the monitor as the original form. On the other hand, 50 IRE, the wall would be gray with half brightness and contrast.

Figure 2: Shape of the composite video signal to a horizontal line showing the signal level (IRE).

Source: Propia

F-Stop

It is the ability of the lens to collect as much light as possible and concentrate on the camera sensor. An F1.4 lens collects light double the F2.0 lens. Therefore, it is important that the manufacturer provides this information in the data sheet.

Color temperature

It is way of express the content spectrum light source. This amounts not only for monitoring video cameras, but also for professional photography, public, residential and artistic lighting etc.

The higher the temperature of colour generated by a light source, the greater the amount of electrons generated, making the sensor of the camera more sensitive.

 

Figure 3: Examples of colour temperature. Source: Julio Ng Photography

Reflection Index

The reflection index of light from an object at the background of the screen is significantly altered by the degree of minimum illumination, because if the object absorbs light, less light is received by the sensor lens and the camera.

Comparison of different models

So the question is: How can I compare these cameras from different manufacturers, when the information and lighting tests information are completely different? There are formulas for converting a given specification of a camera to other parameters such as the F-Stop and Reflection rate considering

the following:

Lux 1: Minimum illumination reported by the manufacturer

F-Stop 1: F-Stop lens informed by the manufacturer

R1: Reflection index of the material reported by the manufacturer to test

Lux 2: Minimum required illumination

F-Stop 2: F-stop of the lens to be used by the client for comparison

R2: Reflection index of the material used by the client for comparison

 

 

Figure 4: Formula for converting a low light camera (1) to required minimum illumination with the new parameters of F-Stop and reflection rate (2).

For IRE

Lux 1: Minimum illumination reported by the manufacturer

IRE 1: Signal level reported by the manufacturer

Lux 2: Minimum required illumination

IRE 2: Signal level used by the client for comparison

 

Figure.5: Formula for converting a low light camera (1) minimum illumination required for a new IRE (2) parameter.

 

Thus, we can verify that the specifications below are references to the same camera:

Camera A: 1 lux (F1.4, 30IRE, 80%)

Camera B: 0.001 lux (F0.75, 10IRE, 1%)