[libcamera-devel] [PATCH v3] libcamera: controls: Add controls for HDR

[David Plowman]

We add an HdrMode control (to enable and disable HDR processing)
and an HdrChannel, which indicates what kind of HDR frame (short, long
or medium) has just arrived.

Currently the HdrMode supports the following values:

* Off - no HDR processing at all.
* MultiExposureUnmerged - frames at multiple different exposures are
  produced, but not merged together. They are returned "as is".
* MultiExposure - frames at multiple different exposures are merged
  to create HDR images.
* SingleExposure - multiple frames all at the same exposure are
  merged to create HDR images.
* Night - multiple frames will be combined to create "night mode"
  images.

Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
Reviewed-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/libcamera/control_ids.yaml | 75 ++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
index f2e542f4..c3232abf 100644
--- a/src/libcamera/control_ids.yaml
+++ b/src/libcamera/control_ids.yaml
@@ -774,6 +774,81 @@ controls:
             Continuous AF is paused. No further state changes or lens movements
             will occur until the AfPauseResume control is sent.
 
+  - HdrMode:
+      type: int32_t
+      description: |
+        Control to set the mode to be used for High Dynamic Range (HDR)
+        imaging. HDR techniques typically include multiple exposure, image
+        fusion and tone mapping techniques to improve the dynamic range of the
+        resulting images.
+
+        When using an HDR mode, images are tagged to indicate which HDR channel
+        (long, medium or short) they come from.
+
+        \sa HdrChannel
+
+      enum:
+        - name: HdrModeOff
+          value: 0
+          description: |
+            HDR is disabled. The HDR channel, if present, will report
+            HdrChannelNone.
+        - name: HdrModeMultiExposureUnmerged
+          value: 1
+          description: |
+            Multiple exposures will be generated in an alternating fashion.
+            However, they will not be merged together and will be returned to
+            the application as they are. Each image will be tagged with the
+            correct HDR channel, indicating what kind of exposure (long, medium
+            or short) it is.  The expectation is that, if necessary, the
+            application can merge them to create HDR images for itself.
+        - name: HdrModeMultiExposure
+          value: 2
+          description: |
+            Multiple exposures will be generated and merged to create HDR
+            images. Each image will be tagged with the HDR channel (long, medium
+            or short) that arrived and which caused this image to be output.
+        - name: HdrModeSingleExposure
+          value: 3
+          description: |
+            Multiple frames all at a single exposure will be used to create HDR
+            images. These images should be reported as all corresponding to the
+            HDR short channel.
+        - name: HdrModeNight
+          value: 4
+          description: |
+            Multiple frames will be combined to produce "night mode"
+            images. Images will be tagged as belonging either to the long,
+            medium or short HDR channel according to the implementation.
+
+  - HdrChannel:
+      type: int32_t
+      description: |
+        This value is reported back to the application so that it can discover
+        whether this capture corresponds to the short or long exposure image (or
+        any other image used by the HDR procedure). An application can monitor
+        the HDR channel to discover when the differently exposed images have
+        arrived.
+
+      enum:
+        - name: HdrChannelNone
+          value: 0
+          description: |
+            This image does not correspond to any of the captures used to create
+            an HDR image.
+        - name: HdrChannelShort
+          value: 1
+          description: |
+            This is a short exposure image.
+        - name: HdrChannelMedium
+          value: 2
+          description: |
+            This is a medium exposure image.
+        - name: HdrChannelLong
+          value: 3
+          description: |
+            This is a long exposure image.
+
   # ----------------------------------------------------------------------------
   # Draft controls section
 
-- 
2.39.2