BLC vs HLC vs WDR

There are many different features that go into security cameras that the average consumer is simply not knowledgeable about. Manufacturers take advantage of this fact and mislabel products they offer, promising features and quality that their cameras can simply not provide. The aim of this article is to educate users about these different features and enable them to make smart, informed purchases when they are looking for security cameras.

Features like Backlight Compensation (BLC), Highlight Compensation (HLC), Wide Dynamic Range (WDR) and others are very important to the quality and clarity of the overall video quality of a camera in different lighting conditions encountered in a single day.  These features are very popular and as a result, cheap camera manufacturers will list these features in their specs to help promote and sell their cameras. The problem is, these features are dependent on the sensor and digital signal processor (DSP) that the camera is built with. Without quality components, cheap security cameras are not going to deliver on the manufacturer's promise, leaving many users disappointed in the overall video quality. When used for actual security applications, these features become incredibly important because they enable the viewer to really see the suspect and what is going on in the area of interest. Use this article as a guide to help you determine what features will be best for your use, and what image sensors and DSP chips to look for when you purchase security cameras. Remember, purchasing quality up front will save you from issues down the road with replacing cameras, troubleshooting issues, and time wasted dealing with under performing cameras.

What is Highlight Compensation (HLC) ?

Highlight compensation is a feature that came out of necessity due to overexposure from strong light sources like headlights or spotlights. This feature senses strong sources of light in video and compensates for exposure on these spots to enhance the overall quality. HLC is very helpful in preventing blinding of security cameras at night time from headlights.  License plate readability is a feature nearly everyone wants and expects from their security cameras placed in parking lots and entry points. Without HLC this is something that is simply impossible due to the bright, glaring nature of headlights. With the type of HLC provided in most security cameras these days it is possible to reduce the glare in video to an extent and make it possible to see license plates on slow moving front approaching vehicles or stationary vehicles. But if license plate capture is a feature you are in need of for vehicles moving faster than 5mph we advise using actual license plate capture cameras that are specifically designed for this purpose and will perform better because they have other features in addition to HLC that aid in plate capture. One such feature is shutter rate control.

What is Backlight Compensation (BLC) ?

Backlight compensation is a feature that camera companies have been utilizing for some time now. When someone is say sitting in front of a window, or coming in from outside, there is a lot of natural light behind this person. When a camera is aimed in their direction, the camera is picking up all this natural light behind them, therefore the object or person in the foreground becomes very dark, almost silhouette like. Such video is not good for security personnel trying to determine who this person is.

BLC is a feature provided by the Digital Signal Processor (DSP) in a security camera that optimizes exposure in the foreground and background of security video. It splits the video scene into different regions, and uses a different exposure for each of these regions. It corrects regions with extremely high or low levels of light to maintain a normal and usable level of light for the object in focus. However, it is important to note that BLC has its limits when correcting exposure in situations where there is an extreme difference in light between the foreground and background. For best results, WDR has become the sought after feature.

What is Wide Dynamic Range (WDR) ?

Similar to BLC in its core idea but overall far more advanced, WDR helps balance washed out video that has a large dynamic range. Dynamic range is a general term for differences in ratios between measurable quantities of something. In WDR this refers to the ratio between the lightest and darkest elements of the image. This is especially prevalent in areas with a lot of natural light like offices or retail stores with large windows. Cameras that have WDR capabilities come with a sensor fitted with two image sensors of the Charge Coupled Device (CCD) type. One of these sensors is for high speed, the other is for low speed image/video capture. They work together to make multiple scans of a scene to provide one balanced and unwashed image that is clear for the user. Two scans are taken of each video frame, instead of one scan like typical cameras. The first scan takes the image in normal light conditions while the other scans the image at high speed to get an image with a strong light in the background.  The image processor in the CCDs takes it from there, and then goes on to combine the two images to form one usable view for the user, incorporating both the indoor and outdoor light and clarity. This feature however, is completely dependent and restricted by the actual image sensor that is built into the camera. This is why it is important to understand the quality needed in the product and make sure that a camera has quality components before you buy it.

What is Digital Wide Dynamic Range (DWDR) ?

DWDR is the manufacturer's answer to providing a key feature cheaply.  DWDR relies on the DSP chip instead of the image sensor to provide WDR. While nice to have, especially instead of not having any similar features, DWDR seems to be inferior overall to WDR. There are a few reasons for this that we will explore. Where WDR uses Double Scan technology, DWDR uses a digital pixel related manipulation feature. It adjusts each individual pixel of the image and calculates exposure accordingly. Its similar to the differences between digital zoom and optical zoom, the original image that it is modifying is better before any digital effects. Therefore, this technique has some limitations. It's been said that DWDR cannot do much for the very bright pixels, and just brightens the dark ones to compensate for exposure differences. The fact that it is intensely manipulating the pixels leads to the overall image being noticeably more grainy and pixelated. Overall DWDR is a feature that is offered to compensate for a lack of actual WDR which requires more costly image sensors to manufacture the camera.

True WDR / Real WDR / Super WDR

Because of all the different types of labels that companies put on their products, it's important to talk about some of the alternative phrasing that is out in the market describing the same features. The term "True WDR" and the like really only refer to one thing, i.e. this is the manufacturer promising you that the WDR feature you are purchasing will actually perform to the specs they have claimed for their product. As mentioned earlier, the limitations of WDR are dependent on the image sensor of the camera. There are so many false promises on the market these days that manufacturers started using these phrases to help sell their products by promising actual quality WDR compared to the lower quality digital alternative DWDR.

Image Sensors and Digital Signal Processors (DSP)

The combination of an Image Sensor and Digital Signal Processor makes up the imaging portion of a security camera. This duo determines what the quality of the camera's video signal will be. If you purchase a camera that has a quality image sensor and DSP, you will overall have better more satisfying video, especially in variable lighting conditions requiring HLC, BLC, and WDR. When looking at a camera's specifications it is important to look for the types of these two components contained within. Understanding their roles in the camera will play a huge a part in your decision to purchase one camera over another. Below we discuss some of the common types of these imaging components.

Digital Signal Processors (DSP)

The DSP is a chip within a security camera to process video picked up by the image pickup device, i.e. the image sensor. Inside of the DSP there are several components that make up the overall operation of the chip.  These include the program memory, the data memory, the compute engine, and software. The software in the DSP processes video signals so they can be analyzed, displayed, or converted into another type. This is a very important component in the surveillance camera that will affect its overall video quality, and it provides advanced imaging features such as HLC, BLC, and WDR.

In analog cameras the DSP simply provides the features mentioned above. In PoE cameras, hdcvi cameras, or other HD over coax cameras the DSP also converts raw video picked up by the imaging device to the appropriate signal type for transmission.

Image Sensors

Image sensors are very important pieces of technology located within your security cameras. The image sensor is the component that captures the light hitting  your camera's lens, turning it into electrical signals which get recorded as video. The two types of sensors used with security cameras are CCD and CMOS sensors. Both have their advantages and disadvantages. Below is a brief summary of each type, and you can find our more about CCD and CMOS image sensors.

CCD Sensors

CCD Sensors are prevalent in analog cameras specifically as a very high quality sensor.  These sensors are what make a Real WDR camera possible along with a DSP like Effio-V. Megapixel CCD sensors are very expensive and because of their cost, most high definition and IP cameras in the consumer market have CMOS sensors instead. This is unfortunate as CMOS sensors lack some features that are only available in CCD sensors. CCD sensors have the highest light sensitivity available, but aren't best for every application. CCD sensors are capable of holding a large signal in any individual pixel and a very low read noise, meaning they have a much larger dynamic range than CMOS sensors. While CMOS may be better for speed related applications, CCD sensors are much better for applications where low noise is needed, specially in low light..

CMOS Sensors

As already stated, most HD and IP cameras are now using CMOS sensors.  CMOS sensors have some advantages and drawbacks when compared to CCD sensors. The rate they can convert images to digital data is much faster than what CCD sensors can provide, so overall they are much faster. They also require lower voltage and have lower power consumption. Unfortunately they generate a lot of electrical noise, leading to a sometimes grainier image. Many manufacturers are incorporating different technologies into their cameras to aid with this however. Also, Real WDR is not available in CMOS sensors at this time, and this is why DWDR and similar techniques are employed through the DSP.

Image Sensor + DSP combinations in IP cameras

In 2015 the CCTV industry saw the most momentum in migration from analog resolution security cameras to high definition. There are 3 different HD over coax technologies available with HDCVI being the most quality controlled. However in the long term, the consensus from manufacturers is that IP cameras will be the future of CCTV since network video is the only modality available to provide sufficient bandwidth for video transmission in resolutions beyond 1080P.

There are several combinations of CMOS sensors and DSP that make up IP cameras available in the market today. Some perform well while most are cheap attempts by Chinese factories at HD video and only a ploy to sell unreliable cameras to end consumers abroad. There are identical looking cameras available in the market because the camera casing is "public," meaning the camera shell is available to any factory or person that can assemble cameras. You can find two identical looking cameras that claim to offer 2 megapixel or higher video, but one camera will be one-half or less the cost of the other. This is because the sensor + DSP combination inside of the cheaper camera will be much inferior, hence cheaper to produce and will produce inferior quality video.

With our vast expertise and experience in the security camera business, we have found that certain combinations are more prevalent than any others. Listed below are the most common CMOS Sensor + DSP combinations in order of best quality video to worst, and not so coincidentally by highest cost to lowest.

SONY CMOS Sensor + SONY DSP - Usually considered the gold standard by factories when comparing Sensor + DSP combinations. We find this combination to produce the best quality video with bright colors, low noise in low light, and offer the most reliable exposure compensation features such as HLC, BLC, and DWDR.

APTINA CMOS Sensor + AMBARELLA DSP - This is considered the best alternative to a all SONY solution because of great video performance, and lower cost. This is the same solution used in most GoPro Cameras. The difference in video quality is negligible, especially when considering the cost. For brands looking for quality, reliable yet affordable IP cameras, this is the solution of choice. The Ambarella DSP has many advanced features including multiple sub-streams, and low bandwidth utilization when compared to cheaper DSP options.

APTINA CMOS Sensor + TEXAS INSTRUMENTS DSP - The Texas Instruments DSP (aka TI) is a cost effective and mediocre quality solution. We have tested cameras with identical sensors with one having an Ambarella DSP versus TI DSP in the other, and found the video noise and clarity to be subpar in the TI version. Despite this, they are still acceptable for affordable ip cameras.

OV CMOS Sensor + TEXAS INSTRUMENTS DSP - OmniVision (OV) used to produce image sensors for iPhone4 and was later acquired by Chinese investors in 2015. Camera factories in China herald the OV sensor as the lowest cost acceptable quality sensor, and anything lower in cost is unacceptable for the foreign market. Using the OV + TI combination it is possible to cut camera production cost in half. We have tested several OV sensor IP cameras and found them to have the lowest level clarity when comparing a similar megapixel resolution Aptina or Sony CMOS sensor.

No Name + TEXAS INSTRUMENTS or No Name DSP - This is the solution you want to avoid where there is a unnamed CMOS sensor in the mix. There are several China and Korea based sensor manufacturers that are trying to make a buck. Their image quality is the lowest we've tested, and so is their cost. It is better to spend $50 more and get a better quality camera instead.