[PATCH v5 1/8] libcamera: controls: Update the ColourTemperature control to be writable

[Stefan Klug]

For manual control it is helpful to be able to specify a fixed colour
temperature. It also provides an easy way to apply the temperature
specific CCMs and colour gains that are contained in the tuning files.

Document this and update the control dependencies.

Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>

---
Changes in v5:
- Improve documentation
---
 src/libcamera/control_ids_core.yaml | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/libcamera/control_ids_core.yaml b/src/libcamera/control_ids_core.yaml
index d45cf8e56187..3795f7169911 100644
--- a/src/libcamera/control_ids_core.yaml
+++ b/src/libcamera/control_ids_core.yaml
@@ -283,7 +283,19 @@ controls:
       description: |
         Enable or disable the AWB.
 
+        When AWB is enabled, the algorithm estimates the colour temperature of
+        the scene, and computes colour gains and the colour correction matrix
+        automatically. The computed colour temperate, gains and correction
+        matrix are reported in metadata. The corresponding controls are ignored
+        if set in a request.
+
+        When AWB is disabled, the colour temperature, gains and correction
+        matrix are not updated automatically and can be set manually in
+        requests.
+
+        \sa ColourCorrectionMatrix
         \sa ColourGains
+        \sa ColourTemperature
 
   # AwbMode needs further attention:
   # - Auto-generate max enum value.
@@ -341,14 +353,25 @@ controls:
         ColourGains can only be applied in a Request when the AWB is disabled.
 
         \sa AwbEnable
+        \sa ColourTemperature
       size: [2]
 
   - ColourTemperature:
       type: int32_t
       description: |
-        Report the estimate of the colour temperature for the frame, in kelvin.
+        Report the current estimate of the colour temperature, in kelvin, for
+        this frame. An implementation may allow this control to be set when AWB
+        is disabled. In that case ColourGains and the ColourCorrectionMatrix get
+        set accordingly. If ColourGains and ColourTemperature are specified at
+        the same time, ColourGains takes precedence. The same applies to
+        ColourCorrectionMatrix.
+
+        The metadata will only report measured colour temperature values when
+        available, even if set manually.
 
-        The ColourTemperature control can only be returned in metadata.
+        \sa AwbEnable
+        \sa ColourCorrectionMatrix
+        \sa ColourGains
 
   - Saturation:
       type: float
@@ -405,6 +428,8 @@ controls:
         stored in conventional reading order in an array of 9 floating point
         values.
 
+        \sa AwbEnable
+        \sa ColourTemperature
       size: [3,3]
 
   - ScalerCrop:
-- 
2.43.0