Wide dynamic range

WDR - Dynamic contrast

WDR mode is a technology that extends the camera’s range, to cover a greater span between the bright and the dark areas in the image.

There are several ways to increase the dynamic range, and many solutions are used in combination to achieve the best result.

Figure 3: The entire dynamic range of a scene.

Figure 4: The dynamic range (shown in red) captured by a non-WDR-capable camera. The area to the left is underexposed, and the area to the right is overexposed.

Figure 5: The greater dynamic range (shown in red) as captured by a WDR-capable camera.

The simplest method of combatting WDR is what Axis calls Dynamic Contrast, a capability built-in to most of our cameras. In this method, the camera’s sensor captures an image with a higher bit depth (an internal property that translates to dynamic range) than what the camera can actually deliver.

The camera then performs advanced tone mapping, in which some brightness levels are dropped, to decrease the bit depth to a format that a computer screen can handle. Both the darkest and the brightest parts are taken into account, resulting in more details at both ends of the scale.

Figure 6: The uppermost bar represents the high bit depth image saved to the sensor. The center bar shows how certain parts of the image are dropped. The lowermost bar shows the output after the tone mapping.

There are two types of tone mapping. In Global Tone mapping, all pixels are handled the same way, meaning that the same levels are removed everywhere in the image. With Local Tone mapping, decisions are made per region in the image, to determine which levels to remove. Local Tone mapping requires much more processor power, but gives a superior result.

WDR - Dynamic capture