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

[Jean-Michel Hautbois]

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.
'''

> 
>>
>> 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) {