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

[Kieran Bingham]

Hi David,

Quoting David Plowman via libcamera-devel (2023-10-05 11:41:33)
> We add an HdrMode control (to enable and disable HDR processing)
> and an HdrChannel, which indicates what kind of HDR frame (short, long
> or otherwise) 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 | 63 ++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> index f2e542f4..e3699e74 100644
> --- a/src/libcamera/control_ids.yaml
> +++ b/src/libcamera/control_ids.yaml
> @@ -774,6 +774,69 @@ 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.
> +
> +      enum:
> +        - name: HdrModeOff
> +          value: 0
> +          description: |
> +            HDR is not enabled.
> +        - 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. 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.
> +        - name: HdrModeSingleExposure
> +          value: 3
> +          description: |
> +            Multiple frames all at a single exposure will be used to create HDR
> +            images.
> +        - name: HdrModeNight
> +          value: 4
> +          description: |
> +            Multiple frames will be combined to produce "night mode" images.

MdrModeMultiExposureUnmerged has been documented to describe what that
is doing. HdrModeMultiExposure, and HdrModeSingleExposure are more self
explanatory - but HdrModeNight might need more explaining.

Does this just mean sequential images are stacked? Are there different
exposures? Are there any other expectations that a user may need or
assumptions they could get wrong?

Or is it just 'Hey do anything you like to make pictures look better at
night time or in low light conditions'?.



> +
> +  - 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).
> +
> +      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.
> +        - name: HdrChannelNight
> +          value: 4
> +          description: |
> +            This frame has been used to produce a "night mode" image.

What does it mean if a 'single' frame has been used to produce a night
mode image. Does that mean it's blended with previous frames? Or is this
frame only 'one' of a set?

"Frame has been used to produce" makes it sound like the result of using
this frame will be output later and maybe this frame should be discarded
because it's not the "final" night mode image ?



> +
>    # ----------------------------------------------------------------------------
>    # Draft controls section
>  
> -- 
> 2.30.2
>