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

[Paul Elder]

Hi Jean-Michel,

On Thu, Nov 11, 2021 at 03:09:19PM +0100, 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.

This is parsed as "this patch removes the early return" and "this patch
computes the gain for each frame".

> 
> Instead of that, introduce a number of startup frames during which the

And this "instead" reads like it contradicts the two points above :/

I think dropping "instead of that" or adding a bit more, like "instead
of the early return" would make it easier to read.

> filter speed is 1.0, meaning we apply instantly the exposure value
> calculated and not a slower filtered one.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

With those clarifications (and the elaboration that you sent to Umang),

Reviewed-by: Paul Elder <paul.elder 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) {
> -- 
> 2.32.0
>