[libcamera-devel] [PATCH v4 05/14] ipa: ipu3: agc: Compute the gain for each frame

[Umang Jain]

Hi JM,

Thank you for the patch.

On 11/11/21 7:39 PM, Jean-Michel Hautbois wrote:
> Now that we have the real exposure applied at each frame, remove the
> early return based on a frame counter and compute the gain for each
> frame.
>
> Instead of that, introduce a number of startup frames during which the
> filter speed is 1.0, meaning we apply instantly the exposure value
> calculated and not a slower filtered one.


To me, it feels a 'because...' is coming at the end of the commit 
message. Perhaps, I don't have enough context, but I assume we want to 
converge fast while startup hence we use speed == 1? If you could add 
the explaination a bit, it would make more complete commit message for 
naive reviewers like me ;-)

>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>

> ---
>   src/ipa/ipu3/algorithms/agc.cpp | 26 +++++++++++---------------
>   1 file changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 83aa3676..74bce7bb 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -45,11 +45,6 @@ namespace ipa::ipu3::algorithms {
>   
>   LOG_DEFINE_CATEGORY(IPU3Agc)
>   
> -/* Number of frames to wait before calculating stats on minimum exposure */
> -static constexpr uint32_t kInitialFrameMinAECount = 4;
> -/* Number of frames to wait between new gain/shutter time estimations */
> -static constexpr uint32_t kFrameSkipCount = 6;
> -
>   /* Limits for analogue gain values */
>   static constexpr double kMinAnalogueGain = 1.0;
>   static constexpr double kMaxAnalogueGain = 8.0;
> @@ -69,10 +64,13 @@ static constexpr double kEvGainTarget = 0.5;
>    */
>   static constexpr uint32_t kMinCellsPerZoneRatio = 255 * 20 / 100;
>   
> +/* Number of frames to wait before calculating stats on minimum exposure */
> +static constexpr uint32_t kNumStartupFrames = 10;
> +
>   Agc::Agc()
> -	: frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
> -	  minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
> -	  currentExposure_(0s), prevExposureValue_(0s)
> +	: frameCount_(0), iqMean_(0.0), lineDuration_(0s), minExposureLines_(0),
> +	  maxExposureLines_(0), filteredExposure_(0s), currentExposure_(0s),
> +	  prevExposureValue_(0s)
>   {
>   }
>   
> @@ -159,6 +157,11 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
>   void Agc::filterExposure()
>   {
>   	double speed = 0.2;
> +
> +	/* Adapt instantly if we are in startup phase */
> +	if (frameCount_ < kNumStartupFrames)
> +		speed = 1.0;
> +
>   	if (filteredExposure_ == 0s) {
>   		/* DG stands for digital gain.*/
>   		filteredExposure_ = currentExposure_;
> @@ -185,13 +188,6 @@ void Agc::filterExposure()
>    */
>   void Agc::computeExposure(IPAFrameContext &frameContext)
>   {
> -	/* Algorithm initialization should wait for first valid frames */
> -	/* \todo - have a number of frames given by DelayedControls ?
> -	 * - implement a function for IIR */
> -	if ((frameCount_ < kInitialFrameMinAECount) || (frameCount_ - lastFrame_ < kFrameSkipCount))
> -		return;
> -
> -	lastFrame_ = frameCount_;
>   
>   	/* Are we correctly exposed ? */
>   	if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1) {