1.11. Camera Control Reference

The Camera class includes controls for mechanical (or equivalent digital) features of a device such as controllable lenses or sensors.

1.11.1. Camera Control IDs

V4L2_CID_CAMERA_CLASS (class)
The Camera class descriptor. Calling ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU for this control will return a description of this control class.
V4L2_CID_EXPOSURE_AUTO
(enum)
enum v4l2_exposure_auto_type -
Enables automatic adjustments of the exposure time and/or iris aperture. The effect of manual changes of the exposure time or iris aperture while these features are enabled is undefined, drivers should ignore such requests. Possible values are:
V4L2_EXPOSURE_AUTO Automatic exposure time, automatic iris aperture.
V4L2_EXPOSURE_MANUAL Manual exposure time, manual iris.
V4L2_EXPOSURE_SHUTTER_PRIORITY Manual exposure time, auto iris.
V4L2_EXPOSURE_APERTURE_PRIORITY Auto exposure time, manual iris.
V4L2_CID_EXPOSURE_ABSOLUTE (integer)
Determines the exposure time of the camera sensor. The exposure time is limited by the frame interval. Drivers should interpret the values as 100 µs units, where the value 1 stands for 1/10000th of a second, 10000 for 1 second and 100000 for 10 seconds.
V4L2_CID_EXPOSURE_AUTO_PRIORITY (boolean)
When V4L2_CID_EXPOSURE_AUTO is set to AUTO or APERTURE_PRIORITY, this control determines if the device may dynamically vary the frame rate. By default this feature is disabled (0) and the frame rate must remain constant.
V4L2_CID_AUTO_EXPOSURE_BIAS (integer menu)

Determines the automatic exposure compensation, it is effective only when V4L2_CID_EXPOSURE_AUTO control is set to AUTO, SHUTTER_PRIORITY or APERTURE_PRIORITY. It is expressed in terms of EV, drivers should interpret the values as 0.001 EV units, where the value 1000 stands for +1 EV.

Increasing the exposure compensation value is equivalent to decreasing the exposure value (EV) and will increase the amount of light at the image sensor. The camera performs the exposure compensation by adjusting absolute exposure time and/or aperture.

V4L2_CID_EXPOSURE_METERING
(enum)
enum v4l2_exposure_metering -
Determines how the camera measures the amount of light available for the frame exposure. Possible values are:
V4L2_EXPOSURE_METERING_AVERAGE Use the light information coming from the entire frame and average giving no weighting to any particular portion of the metered area.
V4L2_EXPOSURE_METERING_CENTER_WEIGHTED Average the light information coming from the entire frame giving priority to the center of the metered area.
V4L2_EXPOSURE_METERING_SPOT Measure only very small area at the center of the frame.
V4L2_EXPOSURE_METERING_MATRIX A multi-zone metering. The light intensity is measured in several points of the frame and the results are combined. The algorithm of the zones selection and their significance in calculating the final value is device dependent.
V4L2_CID_PAN_RELATIVE (integer)
This control turns the camera horizontally by the specified amount. The unit is undefined. A positive value moves the camera to the right (clockwise when viewed from above), a negative value to the left. A value of zero does not cause motion. This is a write-only control.
V4L2_CID_TILT_RELATIVE (integer)
This control turns the camera vertically by the specified amount. The unit is undefined. A positive value moves the camera up, a negative value down. A value of zero does not cause motion. This is a write-only control.
V4L2_CID_PAN_RESET (button)
When this control is set, the camera moves horizontally to the default position.
V4L2_CID_TILT_RESET (button)
When this control is set, the camera moves vertically to the default position.
V4L2_CID_PAN_ABSOLUTE (integer)
This control turns the camera horizontally to the specified position. Positive values move the camera to the right (clockwise when viewed from above), negative values to the left. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive.
V4L2_CID_TILT_ABSOLUTE (integer)
This control turns the camera vertically to the specified position. Positive values move the camera up, negative values down. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive.
V4L2_CID_FOCUS_ABSOLUTE (integer)
This control sets the focal point of the camera to the specified position. The unit is undefined. Positive values set the focus closer to the camera, negative values towards infinity.
V4L2_CID_FOCUS_RELATIVE (integer)
This control moves the focal point of the camera by the specified amount. The unit is undefined. Positive values move the focus closer to the camera, negative values towards infinity. This is a write-only control.
V4L2_CID_FOCUS_AUTO (boolean)
Enables continuous automatic focus adjustments. The effect of manual focus adjustments while this feature is enabled is undefined, drivers should ignore such requests.
V4L2_CID_AUTO_FOCUS_START (button)
Starts single auto focus process. The effect of setting this control when V4L2_CID_FOCUS_AUTO is set to TRUE (1) is undefined, drivers should ignore such requests.
V4L2_CID_AUTO_FOCUS_STOP (button)
Aborts automatic focusing started with V4L2_CID_AUTO_FOCUS_START control. It is effective only when the continuous autofocus is disabled, that is when V4L2_CID_FOCUS_AUTO control is set to FALSE (0).
V4L2_CID_AUTO_FOCUS_STATUS (bitmask)

The automatic focus status. This is a read-only control.

Setting V4L2_LOCK_FOCUS lock bit of the V4L2_CID_3A_LOCK control may stop updates of the V4L2_CID_AUTO_FOCUS_STATUS control value.

V4L2_AUTO_FOCUS_STATUS_IDLE Automatic focus is not active.
V4L2_AUTO_FOCUS_STATUS_BUSY Automatic focusing is in progress.
V4L2_AUTO_FOCUS_STATUS_REACHED Focus has been reached.
V4L2_AUTO_FOCUS_STATUS_FAILED Automatic focus has failed, the driver will not transition from this state until another action is performed by an application.
V4L2_CID_AUTO_FOCUS_RANGE
(enum)
enum v4l2_auto_focus_range -
Determines auto focus distance range for which lens may be adjusted.
V4L2_AUTO_FOCUS_RANGE_AUTO The camera automatically selects the focus range.
V4L2_AUTO_FOCUS_RANGE_NORMAL Normal distance range, limited for best automatic focus performance.
V4L2_AUTO_FOCUS_RANGE_MACRO Macro (close-up) auto focus. The camera will use its minimum possible distance for auto focus.
V4L2_AUTO_FOCUS_RANGE_INFINITY The lens is set to focus on an object at infinite distance.
V4L2_CID_ZOOM_ABSOLUTE (integer)
Specify the objective lens focal length as an absolute value. The zoom unit is driver-specific and its value should be a positive integer.
V4L2_CID_ZOOM_RELATIVE (integer)
Specify the objective lens focal length relatively to the current value. Positive values move the zoom lens group towards the telephoto direction, negative values towards the wide-angle direction. The zoom unit is driver-specific. This is a write-only control.
V4L2_CID_ZOOM_CONTINUOUS (integer)
Move the objective lens group at the specified speed until it reaches physical device limits or until an explicit request to stop the movement. A positive value moves the zoom lens group towards the telephoto direction. A value of zero stops the zoom lens group movement. A negative value moves the zoom lens group towards the wide-angle direction. The zoom speed unit is driver-specific.
V4L2_CID_IRIS_ABSOLUTE (integer)
This control sets the camera's aperture to the specified value. The unit is undefined. Larger values open the iris wider, smaller values close it.
V4L2_CID_IRIS_RELATIVE (integer)
This control modifies the camera's aperture by the specified amount. The unit is undefined. Positive values open the iris one step further, negative values close it one step further. This is a write-only control.
V4L2_CID_PRIVACY (boolean)
Prevent video from being acquired by the camera. When this control is set to TRUE (1), no image can be captured by the camera. Common means to enforce privacy are mechanical obturation of the sensor and firmware image processing, but the device is not restricted to these methods. Devices that implement the privacy control must support read access and may support write access.
V4L2_CID_BAND_STOP_FILTER (integer)
Switch the band-stop filter of a camera sensor on or off, or specify its strength. Such band-stop filters can be used, for example, to filter out the fluorescent light component.
V4L2_CID_AUTO_N_PRESET_WHITE_BALANCE
(enum)
enum v4l2_auto_n_preset_white_balance -
Sets white balance to automatic, manual or a preset. The presets determine color temperature of the light as a hint to the camera for white balance adjustments resulting in most accurate color representation. The following white balance presets are listed in order of increasing color temperature.
V4L2_WHITE_BALANCE_MANUAL Manual white balance.
V4L2_WHITE_BALANCE_AUTO Automatic white balance adjustments.
V4L2_WHITE_BALANCE_INCANDESCENT White balance setting for incandescent (tungsten) lighting. It generally cools down the colors and corresponds approximately to 2500...3500 K color temperature range.
V4L2_WHITE_BALANCE_FLUORESCENT White balance preset for fluorescent lighting. It corresponds approximately to 4000...5000 K color temperature.
V4L2_WHITE_BALANCE_FLUORESCENT_H With this setting the camera will compensate for fluorescent H lighting.
V4L2_WHITE_BALANCE_HORIZON White balance setting for horizon daylight. It corresponds approximately to 5000 K color temperature.
V4L2_WHITE_BALANCE_DAYLIGHT White balance preset for daylight (with clear sky). It corresponds approximately to 5000...6500 K color temperature.
V4L2_WHITE_BALANCE_FLASH With this setting the camera will compensate for the flash light. It slightly warms up the colors and corresponds roughly to 5000...5500 K color temperature.
V4L2_WHITE_BALANCE_CLOUDY White balance preset for moderately overcast sky. This option corresponds approximately to 6500...8000 K color temperature range.
V4L2_WHITE_BALANCE_SHADE White balance preset for shade or heavily overcast sky. It corresponds approximately to 9000...10000 K color temperature.
V4L2_CID_WIDE_DYNAMIC_RANGE (boolean)
Enables or disables the camera's wide dynamic range feature. This feature allows to obtain clear images in situations where intensity of the illumination varies significantly throughout the scene, i.e. there are simultaneously very dark and very bright areas. It is most commonly realized in cameras by combining two subsequent frames with different exposure times. [1]
V4L2_CID_IMAGE_STABILIZATION (boolean)
Enables or disables image stabilization.
V4L2_CID_ISO_SENSITIVITY (integer menu)
Determines ISO equivalent of an image sensor indicating the sensor's sensitivity to light. The numbers are expressed in arithmetic scale, as per ISO 12232:2006 standard, where doubling the sensor sensitivity is represented by doubling the numerical ISO value. Applications should interpret the values as standard ISO values multiplied by 1000, e.g. control value 800 stands for ISO 0.8. Drivers will usually support only a subset of standard ISO values. The effect of setting this control while the V4L2_CID_ISO_SENSITIVITY_AUTO control is set to a value other than V4L2_CID_ISO_SENSITIVITY_MANUAL is undefined, drivers should ignore such requests.
V4L2_CID_ISO_SENSITIVITY_AUTO
(enum)
enum v4l2_iso_sensitivity_type -
Enables or disables automatic ISO sensitivity adjustments.
V4L2_CID_ISO_SENSITIVITY_MANUAL Manual ISO sensitivity.
V4L2_CID_ISO_SENSITIVITY_AUTO Automatic ISO sensitivity adjustments.
V4L2_CID_SCENE_MODE
(enum)
enum v4l2_scene_mode -

This control allows to select scene programs as the camera automatic modes optimized for common shooting scenes. Within these modes the camera determines best exposure, aperture, focusing, light metering, white balance and equivalent sensitivity. The controls of those parameters are influenced by the scene mode control. An exact behavior in each mode is subject to the camera specification.

When the scene mode feature is not used, this control should be set to V4L2_SCENE_MODE_NONE to make sure the other possibly related controls are accessible. The following scene programs are defined:

V4L2_SCENE_MODE_NONE The scene mode feature is disabled.
V4L2_SCENE_MODE_BACKLIGHT Backlight. Compensates for dark shadows when light is coming from behind a subject, also by automatically turning on the flash.
V4L2_SCENE_MODE_BEACH_SNOW Beach and snow. This mode compensates for all-white or bright scenes, which tend to look gray and low contrast, when camera's automatic exposure is based on an average scene brightness. To compensate, this mode automatically slightly overexposes the frames. The white balance may also be adjusted to compensate for the fact that reflected snow looks bluish rather than white.
V4L2_SCENE_MODE_CANDLELIGHT Candle light. The camera generally raises the ISO sensitivity and lowers the shutter speed. This mode compensates for relatively close subject in the scene. The flash is disabled in order to preserve the ambiance of the light.
V4L2_SCENE_MODE_DAWN_DUSK Dawn and dusk. Preserves the colors seen in low natural light before dusk and after down. The camera may turn off the flash, and automatically focus at infinity. It will usually boost saturation and lower the shutter speed.
V4L2_SCENE_MODE_FALL_COLORS Fall colors. Increases saturation and adjusts white balance for color enhancement. Pictures of autumn leaves get saturated reds and yellows.
V4L2_SCENE_MODE_FIREWORKS Fireworks. Long exposure times are used to capture the expanding burst of light from a firework. The camera may invoke image stabilization.
V4L2_SCENE_MODE_LANDSCAPE Landscape. The camera may choose a small aperture to provide deep depth of field and long exposure duration to help capture detail in dim light conditions. The focus is fixed at infinity. Suitable for distant and wide scenery.
V4L2_SCENE_MODE_NIGHT Night, also known as Night Landscape. Designed for low light conditions, it preserves detail in the dark areas without blowing out bright objects. The camera generally sets itself to a medium-to-high ISO sensitivity, with a relatively long exposure time, and turns flash off. As such, there will be increased image noise and the possibility of blurred image.
V4L2_SCENE_MODE_PARTY_INDOOR Party and indoor. Designed to capture indoor scenes that are lit by indoor background lighting as well as the flash. The camera usually increases ISO sensitivity, and adjusts exposure for the low light conditions.
V4L2_SCENE_MODE_PORTRAIT Portrait. The camera adjusts the aperture so that the depth of field is reduced, which helps to isolate the subject against a smooth background. Most cameras recognize the presence of faces in the scene and focus on them. The color hue is adjusted to enhance skin tones. The intensity of the flash is often reduced.
V4L2_SCENE_MODE_SPORTS Sports. Significantly increases ISO and uses a fast shutter speed to freeze motion of rapidly-moving subjects. Increased image noise may be seen in this mode.
V4L2_SCENE_MODE_SUNSET Sunset. Preserves deep hues seen in sunsets and sunrises. It bumps up the saturation.
V4L2_SCENE_MODE_TEXT Text. It applies extra contrast and sharpness, it is typically a black-and-white mode optimized for readability. Automatic focus may be switched to close-up mode and this setting may also involve some lens-distortion correction.
V4L2_CID_3A_LOCK (bitmask)

This control locks or unlocks the automatic focus, exposure and white balance. The automatic adjustments can be paused independently by setting the corresponding lock bit to 1. The camera then retains the settings until the lock bit is cleared. The following lock bits are defined:

When a given algorithm is not enabled, drivers should ignore requests to lock it and should return no error. An example might be an application setting bit V4L2_LOCK_WHITE_BALANCE when the V4L2_CID_AUTO_WHITE_BALANCE control is set to FALSE. The value of this control may be changed by exposure, white balance or focus controls.

V4L2_LOCK_EXPOSURE Automatic exposure adjustments lock.
V4L2_LOCK_WHITE_BALANCE Automatic white balance adjustments lock.
V4L2_LOCK_FOCUS Automatic focus lock.
V4L2_CID_PAN_SPEED (integer)
This control turns the camera horizontally at the specific speed. The unit is undefined. A positive value moves the camera to the right (clockwise when viewed from above), a negative value to the left. A value of zero stops the motion if one is in progress and has no effect otherwise.
V4L2_CID_TILT_SPEED (integer)
This control turns the camera vertically at the specified speed. The unit is undefined. A positive value moves the camera up, a negative value down. A value of zero stops the motion if one is in progress and has no effect otherwise.
[1]This control may be changed to a menu control in the future, if more options are required.