Image quality

Image enhancements

Fluorescent lighting is very common in stores, warehouses and office environments. In this kind of lighting, the lamp turns on and off at a rapid pace, although to the human eye this appears as a steady flow of light. At certain camera shutter speeds, however, this flickering will create an undesirable effect in the video stream. Enabling the flicker-free option in the camera allows it to adjust its shutter speed to avoid the flickering effect. Depending on the geographical location, the power frequency will be either 50 Hz or 60 Hz, and this value must also be set in the camera, to get proper results from the flicker-free setting.

To produce a balanced exposure the camera adjusts the shutter speed and aperture according to the available light. In some scenes, there may be some areas that are much brighter than others, as caused by reflections, strong lights, or sunlight coming through a window. These overly bright areas may cause the camera to lower its exposure settings, thereby making most of the image too dark.

By enabling the backlight compensation setting, the camera will ignore any isolated bright areas and keep the exposure at a suitable level for the darker parts of the scene.

Figure 6: Overly bright areas can trick the camera into lowering its exposure settings, making most of the image too dark. This is solved by enabling the backlight compensation setting in the camera.

The difference between the darkest and brightest parts of a scene is called the dynamic range. If the dynamic range is wider than the capabilities of the camera’s sensor, the dark parts will be rendered as all black, and the bright parts will be all white.

Some cameras feature a Wide Dynamic Range mode (WDR), which uses various techniques to try to compensate for extremes of brightness in the scene. Try this setting if there are very dark and very bright areas in your scene. If possible, try to position and aim your cameras so as to avoid extreme variations in brightness.

Figure 7: The first two images show how the dynamic range in the monitored scene causes parts of the image to be overexposed or underexposed. In the image to the right, WDR dynamic capture has been used, resulting in a balanced image with all areas visible.¬¬

Quality and compression