Auto focus

Topics
	Skip frames
	Hysteresis
	Limit
	Weighted region of interest
	Region of interest presets
	Sharpness algorithm
	Mode
	Peak search algorithm
	Callbacks

Detailed Description

Auto focus

The autofocus controller will automatically adjusts the lens to focus on a subject.

Enabling and automatically disabling the control function

For ongoing adaptations the Continuous mode has to be used so that it responds to deviations from the target value. To disable the control functionality automatically once the target value has been reached, (approximately) use the Once mode.

Configuring the control functions

Skip frames

The Skip frames setting defines how many frames should be skipped. This parameter strongly influences the control speed. Choosing small values can destabilize the automatic control.

Note

For higher frame rates, a larger value should be used for the Skip frames parameter. This reduces the number of automatic adjustments done by the camera.

Hysteresis

Defines the size of the interval range after which the algorithm terminates the search.

Limit

With the minimum and maximum limit the focus search range for the focus_algorithm can be limited. The focus_limit affects whether and where a maximum value is found.

Weighted region of interest

The Weighted Region of Interest (Weighted ROI) is a concept to prioritize certain areas of an image over others. In the context of autofocus systems, the Weighted ROI is used to assign more importance to specific regions of the image, such as where the main subject is likely located, to ensure optimal focus.

Note

• Depending on the acquisition conditions, several "sharpness maximum values" may be possible in the ROI. This may result in an error in control, especially with Continuous mode.
• Small ROIs can cause the focus to fluctuate constantly so that an optimal focus cannot be found.

Region of interest preset

TODO

Sharpness algorithm

Sets the algorithm for the sharpness calculation.

• Auto: Defaults to PEAK_AFL_CONTROLLER_SHARPNESS_ALGORITHM_TENENGRAD
• Tenengrad: Sobel factors in x- and y-direction and summation of the euclidean distances.
• Mean Score: Summation of the difference between two mean values from two pixel values each in x- and y-direction.
• Histogram Variance: Standard deviation of the gray values in the histogram of the mean value.

Peak search algorithm

Sets the algorithm for the maximum value search.

Note

If no maximum value can be found after 300 iterations, the search is aborted and the focus value is reset to the previous value.

• Auto: Defaults to PEAK_AFL_CONTROLLER_ALGORITHM_GOLDEN_RATIO_SEARCH
• Golden Ratio Search: Within the preset interval range, the focus function repeatedly divides into new intervals using the Golden Ratio. The interval range is decreased with each new calculation. This process continues until the interval range is less than or equal to the set hysteresis.
• Hill Climbing Search: Within the preset interval range, the focus function scans the register values for a maximum with medium step width until two falling sharpness values occur at the last two steps. Based on these values and the step width, the interval range and step width are reduced and the scan is repeated within this interval. This process continues until the interval range is less than or equal to the set hysteresis.
• Global Search: Within the preset interval range, the focus function completely scans with medium step width and the maximum that occurred is memorized. Based on the maximum, the interval range and the step width are reduced and the scan is repeated within this interval. This process continues until the interval range is less than or equal to the set hysteresis.
• Full Scan: Within the preset interval range, the focus function scans with a constant step width for an optimal result (step width: hysteresis).

Callback

It is possible to be informed for specific events via callbacks. The following callbacks are available:

• Finished will be called when the controller has reached the target value.
• Processing will be called when the controller has processed an image.

Note

The Finished callback will only be called when the controller runs in Once mode.

Examples

Note

For the automatic host control to work, the frames must be transferred to the manager. To reduce and simplify the sample code, the examples do not check the return values.

    peak_afl_AutoFeatureManager_Create(&hManager, nodemapHandle);
 
    // create a focus controller within our manager
    peak_afl_controller_handle hController = 0;
    peak_afl_AutoFeatureManager_CreateController(hManager, &hController, PEAK_AFL_CONTROLLER_TYPE_AUTOFOCUS);
 
    // run in continuous mode 
    peak_afl_AutoController_Mode_Set(hController, PEAK_AFL_CONTROLLER_AUTOMODE_CONTINUOUS);
 
    // submit the images
    while (acquisitionRunning)
    {
        peak_afl_AutoFeatureManager_Process(hManager, imageHandle);
    }