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Automatic Image Control |
uEye Camera Manual Version 3.80
Automatic Image Control
The uEye driver provides various options to automatically adjust the image capture parameters to the lighting situation. These include:
• | Auto Exposure Shutter (AES) |
• | Auto Gain Control (AGC) |
• | Auto White Balance (AWB) |
• | Auto Frame Rate (AFR) |
The auto functions are used to adjust the average brightness and color rendering of the camera image to their setpoint values, while trying to keep the frame rate at the highest possible value.
All controls are configured using the is_SetAutoParameter() SDK function.
The control of the average brightness is preferably achieved by adjusting the exposure, i.e. you set the highest possible exposure time before gain is controlled. The auto exposure feature always uses the current exposure range which results from the selected pixel clock frequency and the frame rate. You can set separate control range limits for exposure and gain.
The auto gain feature controls the camera master gain in a range from 0-100%. You can set separate control range limits for exposure and gain.
In the UI-112x / UI-512x uEye models with HDR sensor, the auto gain feature controls the white level for UI-112x / UI-512x Application Notes.
Auto Frame Rate (AFR)
With the exposure control function enabled, you can still change the frame rate manually or automatically to maintain a dynamic exposure control range. A lower frame rate allows for longer exposure times, but then the live image display may exhibit jitter. The objective of the automatic frame rate control is to set the frame rate to an optimum value. This way, in all situations, the automatic exposure control can use the required control range at the highest possible frame rate.
Auto White Balance (AWB)
Depending on the lighting source, light can have different color temperatures so that the images may have a color cast. At low color temperatures (e.g. light from incandescent lamps), the white content is offset towards a red hue. At high color temperatures (e.g. light from fluorescent lamps), the white content is offset towards a blue hue.
The white balance control feature uses the RGB gain settings of the camera to correct the white level. This is achieved by adjusting the gain controls within the 0-100% range until the red or blue channel matches the average brightness of the green channel. In order to manually influence the color rendering, you can adjust the setpoint values for the red and blue channels relative to the green channel by using an offset value.
Automatically Disabling the Control Function
You can disable the control functionality automatically once the target value has been reached (API parameters IS_SET_AUTO_WB_ONCE and IS_SET_AUTO_BRIGHTNESS_ONCE). An event / a message notifies the system of this (see also is_InitEvent()). Alternatively, you can keep the control feature enabled so that it responds to deviations from the target value.
You can set the auto function speeds in a 0–100% range. This influences the control increments. High speed (100%) causes a little attenuation of a fast-responding control and vice versa. The control functions for average brightness and for color rendering use separate speeds.
In trigger mode, every frame is evaluated for automatic control. The freerun mode skips a number of frames by default because in that mode, changes to the image parameters only become effective after one or more image captures (see also Applying New Parameters). With the Skip Frames parameter (API parameter IS_SET_AUTO_SKIPFRAMES), you can select how many frames should be skipped in freerun mode (default: 4). This parameter strongly influences the control speed. Choosing small values can destabilize the automatic control.
The automatic control feature uses a hysteresis function for stabilization. Automatic control is stopped when the actual value lies in a range between (setpoint - hysteresis value) and (setpoint + hysteresis value). It is resumed when the actual value drops below (setpoint - hysteresis value) or exceeds (setpoint + hysteresis value). If the hysteresis value is increased, the control function will stop sooner. This can be useful in some situations.
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Using the photometric settings for automatic image control, you can select specific fields of view or areas of interest that you want to use for determining the correct exposure and gain settings.
The is_SetAutoParameter() function provides the following photometric parameters:
None |
The entire field of view is used for metering. |
Center-weighted (CENTER_WEIGHTED) |
Metering is based on the entire field of view, but gives greater emphasis to the center area of the image. |
Spot (CENTER_SPOT) |
Only a small area in the image center is used for metering. |
Portrait (PORTRAIT) |
Metering is based on that part of the field of view that corresponds to the portrait format. |
Landscape (LANDSCAPE) |
Metering is based on that part of the field of view that corresponds to the landscape format. |
This function allows adjusting the results of the automatic brightness controls (AES / AGC). For this purpose, it passes a correction value in the unit EV (exposure value) to the camera. A positive EV makes the images brighter, a negative EV makes them darker. An EV of 1.0 means that image brightness is doubled or halved.
The auto contrast correction can have an effect on the exposure time, gain, or both.
This function adjusts automatic brightness control in the USB uEye XS to reduce the influence of a bright backlight on the control function. This way, you can capture a clearer image of dark objects against bright background.
With the anti flicker function, the frame rate and exposure time settings are adjusted during automatic image control so that flicker from the lighting is reduced in the image.
See also: |