Wide Dynamic Range (WDR) Technology in Surveillance Cameras
The ever-growing advancements in Wide Dynamic Range (WDR) have made it one of the most important features in surveillance cameras. With the help of WDR, cameras can capture images with clarity and detail in environments with both extreme shadows and bright lights. This feature is particularly useful in entrances, areas with large windows, and areas with varied lighting patterns. Prior to the advent of WDR technology, important details in such environments were often lost in images, leading to the inability to assess the situation accurately. With current WDR technology and achieving a real wide dynamic range, this issue has been resolved.
The Evolution of WDR in Network Cameras
As network cameras enter the age of megapixel resolution, their internal sensors are also undergoing changes to meet the demands of higher quality. CMOS sensors, due to their lower cost, are replacing traditional CCD sensors and are slowly becoming the “eyes” of a large number of megapixel network cameras. However, the technology used by these two sensor types often creates challenges that affect WDR performance in low-light conditions. Fortunately, the progress made in combining various CMOS and Digital Signal Processing (DSP) chips has significantly improved WDR performance.
Today, surveillance cameras with WDR that utilize a combination of CMOS and DSP are gradually dominating the market. From a sales perspective, cameras with WDR features are slightly more expensive. The smart WDR technology, now in its third generation, is also known as “real WDR.” In the market today, any camera that produces a dynamic range of over 100 decibels is considered to have “real WDR” and can work with any related WDR application.
The Expanding Applications of WDR
The rapid development of WDR technology has made it an indispensable key technology in surveillance cameras. Under these circumstances, WDR should have been fully developed and stabilized by now. However, in many cameras, WDR is primarily achieved by merging two images. If the DSP chipset used in this combination does not have the necessary processing capabilities, it can result in poor image recovery, weak color reproduction, blurry images, and low quality. Therefore, understanding the applications of WDR is highly important.
What is WDR?
Many users may not have a clear understanding of WDR and its functionality, and may have misconceptions about what this technology can do. Additionally, many manufacturers have their own definitions and terms related to different WDR technologies. In many cases, a manufacturer’s definition of WDR may conflict with another manufacturer’s interpretation (e.g., digital WDR, real WDR, etc.). In simple terms, WDR is the ability to clearly display the details of both the brightest and darkest areas of a scene simultaneously. In other words, WDR technology can reveal the details in high contrast lighting areas. When both a strong light source (like sunlight, light reflection, etc.) and shadowy, dark areas coexist in a scene, it can cause the bright areas to appear as white spots in the image, while the darker areas appear as black holes. Both situations can negatively affect the image quality. Although there are limitations in what cameras can display from overly dark or overly bright areas, these limitations are often related to the dynamic range.
WDR can be seen as a trade-off. In imaging, the primary task has always been to reduce noise and increase signal. The most notable trade-off in WDR occurs between noise and light spots. Reducing noise and achieving a wider dynamic range is possible, but this comes at the cost of creating new spots. All current WDR techniques create new spots.
It is important to note that the concept of dynamic range is defined as a ratio between the darkest and brightest areas of an image (and not a precise value). This ratio is expressed in decibels. The dynamic range ratio in regular surveillance cameras is 10 decibels, while in typical WDR cameras, this value is 48 decibels. The third generation of WDR cameras can achieve a ratio of 95 decibels. With current technology, the maximum achievable dynamic range is over 120 and less than or equal to 130 decibels.
Main Sensor Combinations for WDR Technology
WDR technology uses different combinations of sensors and processors, which can be broadly divided into three categories. The sensor is a very important part of WDR performance. The dynamic range of a camera depends on the sensor. Pairing the chipset with the sensor is equally important. For example, if an old-generation ISP chipset is paired with a new WDR sensor, the WDR performance may not reach its full potential.
Before WDR technology, to cope with problems in environments with varying light patterns, tools like low lux, filters, polarizers, automatic zoom, and backlight compensation were used. Unfortunately, these technologies had limited capabilities. WDR technology has taken a step beyond previous technologies and compensates for what these earlier techniques couldn’t do. These three main combinations are explained below.
CCD Sensor + DSP
The first combination is made up of CCD sensors and DSP chips. This form of WDR is also known as digital WDR. In other words, this combination is a multi-image display method that includes both high and low-speed displays. The first display focuses on the bright areas of the scene to create an image that clearly reveals the details of those areas. This image is stored in a memory buffer. The second, slower display focuses on the dark areas and creates a clear image of their details, which is then stored in the same memory location. After both operations, the two images are merged using DSP to produce an image that shows the details of both the bright and dark areas of the scene.
CMOS Sensor + DSP WDR
The second combination is inspired by the Pixim technology, based on a new CMOS imaging system developed in the 1990s, known as the Digital Pixel System (DPS).
DPS uses a process in which each pixel is displayed individually. Compared to the multi-image DSP method, this technique can provide a wide dynamic range. The processing power of surveillance cameras that use a CMOS + DPS combination can reach up to 95 decibels, and in some cases, even 120 decibels. Additionally, with DPS, the problems of using CCD sensors (such as color fading and limited processing range) are resolved, and it can meet the needs for accurate color reproduction.
DPS technology operates like the eye and brain, allowing the processor and sensor to communicate with each other in a two-way transaction. When DPS processes an image, it simultaneously sends signals to the image sensor, adjusting both the exposure time and the imaging algorithm to achieve smart imaging. As a result, under specific lighting conditions and in certain environments, surveillance cameras that use DPS can capture more complete images with more details and greater realism.
Sony Effio-P WDR
Compared to the two previously mentioned combinations, Sony Effio-P WDR cameras offer more practical results. The Effio-P can synchronize with the latest sensor technologies and support dual-CCD scanning to achieve real WDR, enabling clear image displays in scenes with strong light or black light.
Performance Differences
Although WDR cameras use the same sensor-chipset combinations, their performance can vary significantly. Having a better sensor does not necessarily mean achieving the best WDR performance, as the signal processor system also plays a crucial role in achieving optimal results.
Another key factor is the operating system used with these sensors. Even if the same sensor is used in WDR cameras, the performance will vary depending on whether the ISP or DSP paired with the sensor is different. The operating system can enhance the image by modifying ISP algorithms, but the real difference lies in the hardware solutions used. Since WDR usually processes larger image files, these images naturally require higher capabilities from the DSP.
Some manufacturers add another chipset to facilitate image processing, ensuring better WDR performance. Therefore, to ensure the best WDR performance, it is essential to have proper design, as the system is configured based on this design.
WDR in Video Displays
To properly display WDR videos, several factors need to be considered. Since the dynamic range of standard monitors is 200 to 300 times less than that of WDR cameras, these monitors cannot properly display WDR images. To address this issue, the WDR image is processed through a non-linear process called tone mapping. In this process, pixels are adjusted to reduce the overall contrast while maintaining local contrast. Currently, many manufacturers use local tone mapping technology, which helps optimize pixel images based on the local characteristics of the image, adjusting the brightness in both overly bright and dark areas, making the image suitable for human eyes and displayable on monitors.
Brand Quality
Although WDR technology is rapidly advancing and developing, it cannot yet be compared to human vision capabilities, as the Low-Lux limit is still too high for cameras. The darker the scene, the weaker the performance of WDR technology will be. Many WDR cameras still require BLC to display objects in environments with challenging lighting conditions. Other limitations, such as shutter limits, also exist due to some technological restrictions.
GeoVision, inspired by the Northern Lights (Aurora), which are visible in photos and videos under very low light conditions, has named its Super Low Lux network camera series Aurora. This series reflects the exceptional performance of network cameras in low-light environments.
If an image consists of consecutive frames, movement in the scene always causes noticeable defects in security camera images. Therefore, only cameras from a few leading brands can satisfy users.
The Aurora series sets new standards for night-time surveillance, offering the ability to capture detailed color images of a suspect’s clothing or a fleeing vehicle in very low light at night or in dimly lit environments such as cafes.