Nighttime surveillance is a critical component in security. In this regard, a low light IP camera can play a key role. In this article, we take a closer look at low light security cameras and explore related topics, including the technology behind low light surveillance camera systems.
Source: William Pao, asmag.com
Night vision vs thermal vs infrared (IR) security cameras
There are three main types of cameras used for low light capturing: a specialized low light or night vision camera with lens, sensor and image signal processor catered to low light capturing; IR illuminated and thermal.
Infrared (IR) night vision cameras come with illuminators that can transmit infrared light for detailed low light images. True day/night cameras have an IR cut-off filter that can filter infrared during the daytime. The surveillance cameras feature smart IR technology that adjusts the infrared light output to the scene accordingly. A proper site assessment would be necessary to determine if the maximum illuminator distance is enough to adequately light up the area for low light imagery.
Thermal cameras rely on radiation emitted from the object instead of visible light. The hotter an object is, the more radiation it emits. The heat sensor in the thermal security camera detects heat signatures and renders them as distinct objects in a thermal image. This makes them ideal for monitoring commercial, residential areas or government installations with little to no light or areas with poor visibility due to fog or smoke. New technologies such as bi-spectral cameras, AI and video analytics are making today’s thermal cameras even more powerful, expanding their use in end-user organizations.
What does a night vision camera do
A night vision camera comes with good lowlight capabilities to capture images well during the night and in other challenging lighting conditions. This is important as many criminal activities take place during the night. According to the US Office of Juvenile Justice and Delinquency Prevention, the number of violent crimes committed by adults peaks at 9 p.m. The best night vision security camera, then, can capture good lowlight images that can serve as forensic evidence for law enforcement officers investigating crimes. It should also be noted that besides low light capturing, these low light cameras are beneficial in scenarios where using illumination is not ideal – either due to cost or the need for covert video capture.
Due to the security camera features and characteristics, they are suitable for a range of applications. “Typical applications are places where there is no supplemental lighting or where cameras with integrated or external IR are not desired. Some of these user cases can be critical infrastructure, parks, shops, or city surveillance,” said Aaron Saks, Senior Technical Marketing and Training Manager at Hanwha Techwin.
“The first, most common use case is the need to monitor areas which are subject to lighting fluctuations due to the changing nature of the source, such as outdoor sites and perimeters. In these cases, the movement of the sun determines the lighting conditions and security operators need a camera which can perform well during the day and night,” said Stefan Lundberg, Senior Expert Engineer at Axis Communications.
Lundberg adds: “Another use case is in indoor public areas, such as parking lots which can be extremely bright and dark in the same frame. The challenge here is that cameras are often configured to a certain range of lighting conditions, but when images are underexposed or overexposed it can be impossible to identify objects and people. Technology, such as Wide Dynamic Range (WDR), can solve the issue by applying multiple exposure levels, contrast enhancement, and advanced algorithms that lower noise and increase the image signal.”
Dahua, for example, has recently introduced IP cameras with Smart Dual Illuminators Technology whereby the cameras use IR illumination as their default lighting solution, keeping a discreet watch on scenes. When pre-defined events occur – usually the detection of a person on the scene – the Dahua camera automatically switches from IR to white light illumination, enabling color images to be viewed.
It should be noted that, besides low light capturing, these night vision cameras are beneficial in scenarios where using illumination is not ideal – either due to cost or due to the need for covert video capture for evidence.
How does security camera work at night?
A night vision camera has different modes. In the low light mode, the camera’s backlight compensation (BLC), P-iris control, exposure value (EV), auto-gain control and digital noise reduction features work together to achieve clear color images in low light conditions. In day and night mode, the camera switches to IR mode when illumination drops to a certain lux (usually 5 to 10 lux, around sunset). In IR mode, the camera captures images in black and white. It should be noted from time to time, a phenomenon called IR overshadowing may occur whereby the object becomes too bright to be identifiable. To overcome this, the user can adjust the camera’s EV, BLC as well as overexposure reduction settings.
In low light conditions, the camera can be assisted with an external or built-in illuminator, which can be IR light (invisible) or white light (visible). “A camera’s ‘gain setting’ can change the brightness level of images; however, too much will introduce noise, so it’s important to find the correct balance for an optimum image. IR illuminators can be used to get brighter images in totally dark environments. However, the images need to be acceptable as black and white in this mode,” said Adam Lowenstein, Director of Product Management at i-PRO Americas. “A ‘slow shutter’ helps to further increase sensitivity. However, this comes with a trade-off for frame rate and afterimage blurring of objects in motion. Even a small amount of light can dramatically improve nighttime image quality, so consider installing additional motion sensitive lighting in critical areas.”
“Adding white light to a camera can improve performance if the objects of interest are not too far away. In general, exposure settings are critical: however, there is always a trade-off between image quality and motion blur to consider in the application,” said Sören Litwitz, Head of Product Management for IoT Portfolio at MOBOTIX. “Image enhancements such as WDR, noise reduction, or color enhancements are helpful but may affect motion blur.”
Low light security cameras and Lux ratings
Camera manufacturers often use Lux values/ratings to indicate the minimum illumination necessary for the night vision camera to record video/images of viewable quality. Thus, Lux – a unit of illuminance – refers to how much light is on a given area and gives users an idea of a camera’s low light sensitivity. Bright sunlight, for example, has a Lux of 107,639. As far as low light is concerned, the Lux is 0.108 for full moon, 0.0108 for quarter moon, 0.0011 for starlight and 0.0001 for overcast night.
It may be pertinent at this point to mention that there are Lux-rating disparagers that argue that since Lux measurements or testing are not standardized across brands and cameras might collect light differently, it makes it difficult or (potentially) inaccurate to compare night vision cameras from different manufacturers. Therefore buyers should use this as a reference, but not an absolute since other important factors impact overall low light performance.
What is a good lux rating for a night vision security camera?
An IP camera working in low light with IR capability can capture black and white images in as low as 0.0001 Lux. However, capturing color in darkness has become an increasingly important trend as color provides more forensic information. The best night vision security camera, then, can take good color images even during extremely low light conditions.
“Standard low light cameras typically are below 1 Lux. Special low light cameras can go as low as 0.006 Lux or even 0.004 Lux, all while delivering color images,” Saks said.
Factors that determine the low light performance of a camera
There are three primary factors that determine the low light performance of a camera. These are:
- Lens
- Image sensor
- Image signal processor
Below we take a closer look at each.
Lens
An IP camera with good low light capabilities begins with the lens, which determines how much light can enter the camera. That said, it’s important to take note of the f-stop value of the lens.
“When looking at performance in low-light conditions, it is important to be sure that cameras are fitted with a suitable lens,” Lundberg said. “A lower f-stop value means the lens has a wider maximum aperture and will perform better in low light. Some cameras have the ability to automatically adjust the aperture (also known as the iris) depending on the available light in the scene, making these models suitable for different types of scenarios.”
Image sensor
Once light enters through the lens it hits the image sensor, which converts light into electric signals. There are two main types of image sensors: CCD and CMOS. CCD stands for charged-coupled device. Its advantages include good performance in low light conditions, good WDR and low noise. Disadvantages include high power consumption and higher cost. CMOS stands for complementary metal-oxide-semiconductor. Its advantages include high resolution, excellent color and cost-effectiveness. Disadvantages include high noise and moderate sensitivity.
For CMOS, it’s important to mention Sony’s STARVIS and STARVIS 2 technologies which are specifically developed for CMOS image sensors. They deliver high image quality in the visible light as well as near infrared light regions. STARVIS 2 further offers the high dynamic range (AD 12bit) of more than 8 dB in a single exposure, wider than the STARVIS pixel of the same size.
When it comes to image sensors for the best low light security cameras, size matters.
“The larger the sensor is, the more light it can collect which directly contributes to better low light performance. A highly sensitive image sensor is also required, but it must also have a balanced performance and not introduce too much noise into the signal,” Lowenstein said.
“Lowlight cameras will have specifically designed sensors that are larger in general, as well as larger pixels, all to capture more light. Often these sensors measure from 1/2” to 1” in size,” Saks said. “In addition, the design of the sensor is such that heat is carried away from the pixels to prevent the heat from being interpreted as noise in the image. These attributes improve sensitivity as well as signal to noise ratio.”
Image signal processor
Finally, for a good IP camera working in low light, its image signal processor also plays a big role. “The quality of the image often relies – at least in part – on sophisticated image processing capabilities, especially advanced noise filtering. Most scenes will have some variation in lighting conditions and advanced image-processing algorithms mean instantaneous adjustment to rapidly changing light. For example, as vehicles and trains move across the landscape – particularly when they enter and exit tunnels,” Lundberg said.
“Quality Image processing algorithms are paramount to generating good quality images in low light. Color information is very important for security use cases, so it’s important that even in lowlight environments, color information is preserved. Good signal processing should be able to brighten images (adding gain) without introducing too much noise. AI-based object detection further complements signal processing by informing the algorithms about detected objects and their motion for further image enhancement,” Lowenstein said.
3 key questions to choose the right low light security camera
When picking the best night vision security camera, three important questions need to be answered:
Does the user want to record low light video in color or black and white?
How will the night vision camera be positioned and what type of scene will it monitor?
Does the user have specific requirements or needs?
When picking the best night vision security camera, a place to start is to decide whether the user wants to record low light video in color or black and white.
“If a user doesn’t mind images in black and white at night, they can choose cameras from a wide range of IR-LED equipped models. If color images are required 24/7, we recommend a model which supports lower minimum illumination (lower lux numbers in the specification),” Lowenstein said.
Another factor to consider is the intended position of the camera and scene to monitor. “This will not only inform the decision on the best lowlight camera, but whether auxiliary lighting will need to be installed. The user may require detail to aid identification or simply to confirm the presence of an intruder. It may be that an alternative – such as thermal or radar – is better suited,” Lundberg said.
Finally, picking the best night vision security camera requires a careful assessment of the user scenario and what the user’s needs are
“There is no general answer to this question. It always depends on the individual scene and the intention of the user. The use and availability of white light or IR lighting directly in the camera can be helpful – especially if the objects are not too far away. Otherwise, it’s a matter of considering the sensors and available sensor/low light specifications of the camera and deciding how the camera fits in based on the desired scenario,” Litwitz said. “As with all other video surveillance cameras, arguments like cyber security, robustness, and durability are always issues. Less maintenance means saving money. Also, the flexibility and modularity of systems play a significant role.”
