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Extended dynamic range

In slow scientific applications such as astronomy, achieving excellent dynamic range is crucial, as details in the dark areas of an image could be just as important as those in the brighter sections and minimum differences in the grey values should be visible. These cameras often deliver true 14 or 16 bits of dynamic range.

For industrial use, a wide dynamic range is for example an issue in the inspection of very bright scenes, where details of the process, as well as high richness of background details are required. A typical vision camera with 8 or 10 bits of dynamic range would only be able to see either the dark or bright areas with any detail. Using special support circuits or signal processing, cameras are able to acquire and output an increased dynamic range. Several technologies are available to achieve this:

Multiple exposure

With a linear sensor a sequence of images with different exposure times is acquired. These images are combined to an HDR image.

Interleaved exposure

Some sensors can be used with an interleaved exposure mode. Odd and even lines are using different exposure times. These lines can be combined to an HDR image directly on the chip (e.g. with vertical Binning), by processing in an FPGA or on the host.

Multi-slope/piecewise linear response

This technology is available for some CMOS sensors. It is based on a reset pulse which is applied with different levels at selectable times during the total exposure time. Typically this reset can be done 1-2 times during one exposure period. The level of the reset pulse and the position relative to the exposure time defines the result of the HDR compression. The image below shows a typical sample of this mode: