[libcamera-devel] [PATCH v3 01/19] ipa: ipu3: Document IPAIPU3 class interface

[Umang Jain]

Hello JM,

Thank you for the patch.

On 10/22/21 8:42 PM, Jean-Michel Hautbois wrote:
> The IPU3 IPA is maturing to a modular and extensible system capable of
> handling specific algorithms for the processing blocks on the ImgU.
>
> Provide a top-level class documentation to provide an overview of the
> IPA, detailing what events are used and what algorithms are currently
> supported, as well as the limitations currently imposed.
>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>
> ---
>   src/ipa/ipu3/ipu3.cpp | 64 +++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 64 insertions(+)
>
> diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
> index 65d3fd2c..b5438ed1 100644
> --- a/src/ipa/ipu3/ipu3.cpp
> +++ b/src/ipa/ipu3/ipu3.cpp
> @@ -179,6 +179,70 @@ using namespace std::literals::chrono_literals;
>   
>   namespace ipa::ipu3 {
>   
> +/**
> + * \brief The IPU3 IPA implementation
> + *
> + * The IPU3 Pipeline defines an IPU3-specific interface for communication
> + * between the PipelineHandler and the IPA module.
> + *
> + * We extend the IPAIPU3Interface to implement our algorithms and handle events
> + * from the IPU3 PipelineHandler to satisfy requests from the application.
> + *
> + * At initialisation time, a CameraSensorHelper is instantiated to support
> + * camera-specific calculations, while the default controls are computed, and
> + * the algorithms are constructed and placed in an ordered list.
> + *
> + * The IPU3 ImgU operates with a grid layout to divide the overall frame into
> + * rectangular cells of pixels. When the IPA is configured, we determine the
> + * best grid for the statistics based on the pipeline handler Bayer Down Scaler
> + * output size.
> + *
> + * Two main events are then handled to operate the IPU3 ImgU by populating its
> + * parameter buffer, and adapting the settings of the sensor attached to the
> + * IPU3 CIO2 through sensor-specific V4L2 controls.
> + *
> + * When the event \a EventFillParams occurs we populate the ImgU parameter
> + * buffer with settings to configure the device in preparation for handling the
> + * frame queued in the Request.
> + *
> + * When the frame has completed processing, the ImgU will generate a statistics
> + * buffer which is given to the IPA as part of the \a EventStatReady event. At
> + * this event we run the algorithms to parse the statistics and cache any
> + * results for the next \a EventFillParams event.
> + *
> + * The individual algorithms are split into modular components that are called
> + * iteratively to allow them to process statistics from the ImgU in a defined
> + * order.
> + *
> + * The current implementation supports three core algorithms:
> + * - Automatic white balance (AWB)
> + * - Automatic gain and exposure control (AGC)
> + * - Tone mapping (Gamma)
> + *
> + * AWB is implemented using a Greyworld algorithm, and calculates the red and
> + * blue gains to apply to generate a neutral grey frame overall.
> + *
> + * AGC is handled by calculating a histogram of the green channel to estimate an
> + * analogue gain and shutter time which will provide a well exposed frame. A
> + * low-pass IIR filter is used to smooth the changes to the sensor to reduce
> + * perceivable steps.
> + *
> + * The Tone mapping algorithm provides a gamma correction table to improve the
> + * contrast of the scene.
> + *
> + * The IPU3 ImgU has further processing blocks to support image quality
> + * improvements through bayer and temporal noise reductions, however those are
> + * not supported in the current implementation, and will use default settings as
> + * provided by the kernel driver.
> + *
> + * Demosaicing is operating with the default parameters and could be further
> + * optimised to provide improved sharpening coefficients, checker artifact
> + * removal, and false color correction.
> + *
> + * Additional image enhancements can be made by providing lens and
> + * sensor-specific tuning to adapt for Black Level compensation (BLC), Lens
> + * shading correction (SHD) and Color correction (CCM).
> + */
>   class IPAIPU3 : public IPAIPU3Interface
>   {
>   public: