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

[Kieran Bingham]

Quoting Umang Jain (2021-11-12 08:48:44)
> Hi JM,
> 
> On 11/12/21 2:17 PM, Jean-Michel Hautbois wrote:
> > Hi Umang
> >
> > On 12/11/2021 09:37, Umang Jain wrote:
> >> 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 ;-)
> >
> > Would it help ?
> > '''
> > 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. This is used to have a faster
> > convergence, and those frames may ultimately be dropped.

That sounds like it might already exist in the code ... perhaps:

"""
and those frames may be dropped in a future development to hide the
convergance process from the viewer.
"""

> > '''
> 
> 
> Yes, this would help. Thank you.
> 
> >
> >>
> >>>
> >>> 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) {