AP0100CS datasheet(27/73 Pages) ONSEMI

27 / 73 page

AP0100CS/D Rev. 6, Pub. 1/16 EN

©Semiconductor Components Industries, LLC,2016.

AP0100CS HDR: Image Signal Processor (ISP)

Camera Control and Auto Functions

Auto Exposure

The auto exposure algorithm optimizes scene exposure to minimize clipping and satu-

ration in critical areas of the image. This is achieved by controlling exposure time and

analog gains of the external sensor as well as digital gains applied to the image.

Auto exposure is implemented by a firmware algorithm that is running on the

embedded microcontroller that analyzes image statistics collected by the exposure

measurement engine, makes a decision, and programs the sensor and color pipeline to

achieve the desired exposure. The measurement engine subdivides the image into 25

windows organized as a 5 x 5 grid.

Figure 17:

5 x 5 Grid

AE Track Driver

Other algorithm features include the rejection of fast fluctuations in illumination (time

averaging), control of speed of response, and control of the sensitivity to small changes.

While the default settings are adequate in most situations, the user can program target

brightness, measurement window, and other parameters described above.

The driver changes AE parameters (integration time, gains, and so on) to drive scene

brightness to the programmable target.

To avoid unwanted reaction of AE on small fluctuations of scene brightness or momen-

tary scene changes, the AE track driver uses a temporal filter for luma and a threshold

around the AE luma target. The driver changes AE parameters only if the filtered luma is

larger than the AE target step and pushes the luma beyond the threshold.

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