[libcamera-devel] [PATCH v2 05/14] ipa: ipu3: agc: Compute the gain for each frame

[Jean-Michel Hautbois]

Hi Kieran,

On 10/11/2021 23:02, Kieran Bingham wrote:
> Quoting Jean-Michel Hautbois (2021-11-10 19:58:52)
>> 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.
>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois 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 2bf68e04..133f5931 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),
> 
> I see frameCount_ is initialised to zero here...
> 
> 
>> +         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;
> 
> And it's used to determine how long into startup we are.
> 
> Is it ever set to 0 on start/stop/configure operations that would
> necessitate re-evaluating the whole startup procedure like this?
> 
> I can't see anything resetting it - and we don't destroy and reconstruct
> the objects so it isn't going to be re-initialised.
> 
> This may be a distinctly separate (and pre-existing) bug, and likely
> warrant a patch or fix of its own.
> 
> I wonder if we should instead be passing in the frame/sequence count for
> all algorithm operations.  That (should?) be reset to zero when
> starting/stopping I think ...
> 

We could add the frameId in the frameContext, and fill it in 
EventStatReady. That would solve the issue and remove the frameCount_ at 
the same time ?

> Even with that limitation, I'm tempted to say this should still go in
> and the count can be fixed on top. I think this is still an improvement.
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
>> +
>>          if (filteredExposure_ == 0s) {
>>                  /* DG stands for digital gain.*/
>>                  filteredExposure_ = currentExposure_;
>> @@ -186,13 +189,6 @@ void Agc::filterExposure()
>>    */
>>   void Agc::computeExposure(uint32_t &exposure, double &analogueGain)
>>   {
>> -       /* 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
>>