* - ``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.

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_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.

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_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_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_ISO_SENSITIVITY_MANUAL``
  - Manual ISO sensitivity.
* - ``V4L2_CID_ISO_SENSITIVITY_AUTO``
  - Automatic ISO sensitivity adjustments.

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:

\small

* - ``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.

\normalsize

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_CAMERA_ORIENTATION_FRONT``
  - The camera is oriented towards the user facing side of the device.
* - ``V4L2_CAMERA_ORIENTATION_BACK``
  - The camera is oriented towards the back facing side of the device.
* - ``V4L2_CAMERA_ORIENTATION_EXTERNAL``
  - The camera is not directly attached to the device and is freely movable.

For a precise definition of the sensor mounting rotation refer to the
extensive description of the 'rotation' properties in the device tree
bindings file 'video-interfaces.txt'.

A few examples are below reported, using a shark swimming from left to
right in front of the user as the example scene to capture. ::

             0               X-axis
           0 +------------------------------------->
             !
             !
             !
             !           |\____)\___
             !           ) _____  __`<
             !           |/     )/
             !
             !
             !
             V
           Y-axis

Example one - Webcam

Assuming you can bring your laptop with you while swimming with sharks,
the camera module of the laptop is installed on the user facing part of a
laptop screen casing, and is typically used for video calls. The captured
images are meant to be displayed in landscape mode (width > height) on the
laptop screen.

The camera is typically mounted upside-down to compensate the lens optical
inversion effect. In this case the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION control is 0, no rotation is required to
display images correctly to the user.

If the camera sensor is not mounted upside-down it is required to compensate
the lens optical inversion effect and the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION control is 180 degrees, as images will
result rotated when captured to memory. ::

             +--------------------------------------+
             !                                      !
             !                                      !
             !                                      !
             !              __/(_____/|             !
             !            >.___  ____ (             !
             !                 \(    \|             !
             !                                      !
             !                                      !
             !                                      !
             +--------------------------------------+

A software rotation correction of 180 degrees has to be applied to correctly
display the image on the user screen. ::

             +--------------------------------------+
             !                                      !
             !                                      !
             !                                      !
             !             |\____)\___              !
             !             ) _____  __`<            !
             !             |/     )/                !
             !                                      !
             !                                      !
             !                                      !
             +--------------------------------------+

Example two - Phone camera

It is more handy to go and swim with sharks with only your mobile phone
with you and take pictures with the camera that is installed on the back
side of the device, facing away from the user. The captured images are meant
to be displayed in portrait mode (height > width) to match the device screen
orientation and the device usage orientation used when taking the picture.

The camera sensor is typically mounted with its pixel array longer side
aligned to the device longer side, upside-down mounted to compensate for
the lens optical inversion effect.

The images once captured to memory will be rotated and the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION will report a 90 degree rotation. ::


             +-------------------------------------+
             |                 _ _                 |
             |                \   /                |
             |                 | |                 |
             |                 | |                 |
             |                 |  >                |
             |                <  |                 |
             |                 | |                 |
             |                   .                 |
             |                  V                  |
             +-------------------------------------+

A correction of 90 degrees in counter-clockwise direction has to be
applied to correctly display the image in portrait mode on the device
screen. ::

                      +--------------------+
                      |                    |
                      |                    |
                      |                    |
                      |                    |
                      |                    |
                      |                    |
                      |   |\____)\___      |
                      |   ) _____  __`<    |
                      |   |/     )/        |
                      |                    |
                      |                    |
                      |                    |
                      |                    |
                      |                    |
                      +--------------------+

As modes differ for each sensor, menu items are not standardized by this
control and are left to the programmer.