What is BLC, HLC, True WDR & HDR on a Security Camera?

Nowadays, security cameras are an absolute necessity, regardless of whether it’s your home or workplace. Cameras have a very hard time adjusting to the environment especially when the lighting conditions are constantly changing. Fortunately, hardware and software improvements such as BLC, HLC, and WDR have been developed to overcome this. 

In this article, we’ll talk about how these technologies help security cameras improve their footage.

What is BLC?

BLC stands for “Backlight Compensation.” It is a setting used in security cameras to improve the clarity of shadows (or Backlights) of an image. 

Most modern cameras can automatically balance the contrast (to improve the clarity of the image). So when the camera is exposed to a low light environment, it opens up and collects more light, and vice versa. 

Because of this feature, it’s very easy to manipulate the cameras to under-expose certain regions of the image by shining a light on them. To avoid this happening, security cameras have introduced the BLC feature. 

When the BLC feature is turned on, it doesn’t try to balance out the contrast of the entire image at once. The image is separated into different sections and the exposure is increased separately. This prevents the entire image from getting over-exposed, and instead, the darker regions of the image (Backlights/Shadows) become clearer while the highlights (brighter areas) become over-exposed without affecting the entire image. 

What is HLC?

HLC (as you’re already figured out by now) is the other end of the spectrum. It stands for “Highlight Compensation” and it’s used to reduce the over-exposure of bright and reflective objects.

When there are reflective surfaces and/or light sources (such as shiny surfaces and headlights from vehicles) the resulting image captured by the security camera can exhibit a lot of “glare” and reduce the clarity of the image.

As is the case with HLC, the image is segmented into several sections, and the exposure of each section is reduced separately. This gets rid of the glare (to a significant extent) and improves the readability of the image. 

A very practical use case of HLC is when it is used to reduce the glare caused by headlights of passing vehicles. With HLC turned on, the darker regions of the image remain distinct while the glare is localized only to the headlights, allowing the camera to capture important information such as the number plates and faces of drivers/pedestrians. 

What is WDR?

Now after we’ve covered HLC and BLC, you might be wondering about how security cameras can find the perfect balance between these two. That’s where WDR (Wide Dynamic Range) comes into play.

WDR is considered as the more advanced and “balanced” setting for both BLC and HLC. WDR aims to improve the exposure of low-light elements such as backlights/shadows while also maintaining the clarity of the over-exposed regions. 

For example, if we consider a security camera installed inside a room with windows (where the windows and the outside are also meant to be observed) the BLC setting will improve the inside of the room, but it will brighten the light coming in from the windows to the point where it becomes unreadable. 

With WDR technology, the camera uses two different sensors to capture the image at two different exposure levels and stitches them together. The resulting image is a very clear image showing the inside of the room and the outside details with the same level of accuracy, i.e, there are no over-exposed or under-exposed parts in the image blocking out any vital information. 

Therefore, the image is considered to have a wider dynamic range. Hence, the images that it captures have higher intensity levels and the ability to display a wider range of colors.

Why is WDR measured in decibels?

WDR is a very important feature and it is used in almost every modern security camera because of its powerful feature to provide images very clearly regardless of fluctuating exposure levels. 

With that being said, experts have improved WDR technology in cameras. More specifically improvements were done to the light sensors and the hardware of the camera. Therefore, some cameras have improved hardware capabilities, allowing them to capture more “nuanced” colors and brightness levels. 

Experts rated this ability by the amount of maximum radiance that a camera is capable of capturing. After which, they developed a logarithmic ratio of the maximum and minimum radiance that a camera can capture from a scene. 

Since this was a logarithmic ratio, the unit of measurement was decibels. (dB) It is a common form of measurement used for many other applications that deal with signals.

The most common WDR value was 60dB, which meant that the camera was had a ratio of 1000:1, and higher decibel values (such as 120dB, 140dB) meant that the cameras had an even wider dynamic range. This is used as a spec to evaluate security cameras, and the higher the HDR dB value, the better the camera.

What is DWDR/HDR?

While the WDR feature requires hardware to operate (specifically two different light sensors) DWDR and HDR are completely software-based technologies that are used to improve the clarity and variety of colors in the image. 

In terms of function: DWDR and HDR are the same. However, HDR was coined as an improvement because it was used to advertise the DWDR feature to smartphones. Before smartphones had the fast processing power to manage HDR algorithms in real-time it was used in photo editing software to improve the colors and make images look more vibrant.

Since they are software algorithms, they are also called “post-processing” techniques and although they aren’t as powerful as the hardware-based WDR, they have their uses in TVs, Monitors, Smartphones, and other entertainment devices. 

The difference between DWDR/HDR and WDR

WDR technology can only be used with the proper hardware while DWDR/HDR is a software-based preprocessing feature that can be applied to any image after it has been captured. 

Most experts consider that WDR or “True WDR” is the better feature since it develops the photo at the hardware stage. This allows the image to be captured with better colors and intensity levels right at its inception. An image with WDR is always going to have a “wider” range of colors and brightness levels, making it a more accurate representation of a scene than an image that is captured without WDR technology. In other words, images captured using WDR contain more details and more information, regardless of whether they were processed using DWDR/HDR technology. 

Benefits of these features for camera surveillance

Although BLC and HLC are rudimentary technologies when compared with WDR, they all play a part in improving the clarity and information of your security camera’s footage. 

With BLC, you don’t need to worry about the brighter regions ruining the darker regions in a scene, and with HLC you won’t miss out on details that could get overwhelmed by the intense brightness or reflections from a light source.

And finally, to bring it all together, there’s WDR. This technology improves the details in an image without over-exposing or under-exposing any specific region. Therefore, with WDR technology you can have your windows and also be able to see what’s happening inside and outside very clearly. 


For beginners, understanding these image processing technologies might be a bit daunting. So if you are having concerns about the need to pick out an expensive security camera with all of these high-end features, you should always refer to where you are thinking of installing this camera, and what sort of information you are hoping to gather. Fortunately, most cameras used in modern security systems have these features, so you won’t have to worry about it unless you are “Doing It Yourself.”



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