In many practical surveillance applications, the intensity of illumination with a scene can vary excessively. Images taken by standard cameras always seem to have an overexposed foreground or too dark a background due to the limitation of a camera sensors’ sensitivity. Over the course of a day, the situation can change with different areas of the scene being over or underexposed. What is required in this situation is a Wide Dynamic Range (WDR) camera. This article will explain what the WDR does on CCTV cameras and why you may need a camera with this feature.
The Dynamic Range itself is the difference in light levels in an image, between the darkest and the brightest areas. On an overcast day with little sun and few shadows, there will be a fairly low dynamic range, i.e. there will be no areas of deep black and no extreme bright spots. On a sunny day, however, in a scene with distinct shadows, there will be a greater difference between the brightest and darkest areas, and this is what we call a wide dynamic range or WDR (also known as High Dynamic Range, or HDR).
Cameras with WDR technology have advanced sensors that can produce a wider range of lighting, allowing them to record in a higher light depth. Along with recording a larger range of lighting more accurately, WDR-enhanced cameras have two other ways of balancing light for better images. Tone mapping lets the camera or software automatically brighten dark areas and darken light areas.
Alternatively, the camera will capture several shots of the scene at different exposure levels. This creates overexposed and underexposed identical images, which the camera will combine. It takes the most balanced parts of both images, creating the recorded image you see. This method requires an extremely fast and light-sensitive sensor, however, and is only available on advanced professional cameras.
How Wide Dynamic Range can help you?
Cameras with wide dynamic range are great for many tricky lighting situations:
• Lobbies and showrooms with many windows where the contrast between natural light and indoor light causes bright and dark areas.
• Indoor recording, where the light when a door opens may make the person and their clothing unrecognizable.
• Nighttime recording, where non-IR lighting may overexpose some areas while leaving other areas dark.
What is Digital Wide Dynamic Range (DWDR)?
DWDR is the manufacturer’s answer to providing a key feature cheaply. DWDR relies on the 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. 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. It’s 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. 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.