[libcamera-devel] [PATCH v3 12/14] ipa: ipu3: agc: Refactor condition on exposure correction

[Jean-Michel Hautbois]

Hi Laurent,

On 22/10/2021 06:27, Laurent Pinchart wrote:
> Hi Jean-Michel,
> 
> On Thu, Oct 21, 2021 at 06:43:59PM +0200, Jean-Michel Hautbois wrote:
>> Until now, we can't know when the exposure and gains applied in the
>> IPAIPU3::setControls() are really applied (it can be several frames). We
>> don't want to use the values calculated as if they are already applied,
>> and this is done by testing the frame number.
>>
>> When the exposure is estimated, we verify if it changed enough for
>> exposure and gain to be updated.
>>
>> Keep the indentation level removal and simply return when the change is
>> so small there is no need to apply the newly calculated value.
> 
> The first two paragraph seems unrelated to the version of this patch,
> and the "keep" in the third paragraph refers to how this has changed
> compared to v2. Please rewrite the commit message to correspond to the
> code changes.

Let's try:
'''
Each time we test the brightness with the desired the target, we verify
if the change is small enough to consider that we are correctly exposed
or not. Simplify the reading by removing one level of indentation, and
returning from the function when the change is too small.
'''

> 
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
>> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>> ---
>>   src/ipa/ipu3/algorithms/agc.cpp | 91 ++++++++++++++++-----------------
>>   1 file changed, 45 insertions(+), 46 deletions(-)
>>
>> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
>> index 43ef89df..7ff3029b 100644
>> --- a/src/ipa/ipu3/algorithms/agc.cpp
>> +++ b/src/ipa/ipu3/algorithms/agc.cpp
>> @@ -138,60 +138,59 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
>>   	if ((frameCount_ < kInitialFrameMinAECount) || (frameCount_ - lastFrame_ < kFrameSkipCount))
>>   		return;
>>   
>> -	/* Are we correctly exposed ? */
>> -	if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1) {
>> -		LOG(IPU3Agc, Debug) << "!!! Good exposure with iqMean = " << iqMean_;
>> -	} else {
>> -		double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
>> +	if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1)
>> +		return;
>>   
>> -		/* extracted from Rpi::Agc::computeTargetExposure */
>> -		utils::Duration currentShutter = exposure * lineDuration_;
>> -		currentExposureNoDg_ = currentShutter * analogueGain;
>> -		LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
>> -				    << " Shutter speed " << currentShutter
>> -				    << " Gain " << analogueGain
>> -				    << " Needed ev gain " << evGain;
>> +	double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
>>   
>> -		currentExposure_ = prevExposureValue_ * evGain;
>> -		utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
>> -		utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
>> +	/* extracted from Rpi::Agc::computeTargetExposure */
>> +	utils::Duration currentShutter = exposure * lineDuration_;
>> +	currentExposureNoDg_ = currentShutter * analogueGain;
>> +	LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
>> +			    << " Shutter speed " << currentShutter
>> +			    << " Gain " << analogueGain
>> +			    << " Needed ev gain " << evGain;
>>   
>> -		utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
>> -		currentExposure_ = std::min(currentExposure_, maxTotalExposure);
>> -		LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
>> -				    << ", maximum is " << maxTotalExposure;
>> +	currentExposure_ = prevExposureValue_ * evGain;
>> +	utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
>> +	utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
>>   
>> -		/* \todo: estimate if we need to desaturate */
>> -		filterExposure();
>> +	utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
>> +	currentExposure_ = std::min(currentExposure_, maxTotalExposure);
>> +	LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
>> +			    << ", maximum is " << maxTotalExposure;
>>   
>> -		utils::Duration exposureValue = filteredExposure_;
>> -		utils::Duration shutterTime = minShutterSpeed;
>> +	/* \todo: estimate if we need to desaturate */
>> +	filterExposure();
>>   
>> -		/*
>> -		 * Push the shutter time up to the maximum first, and only then
>> -		 * increase the gain.
>> -		 */
>> -		shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
>> -							  minShutterSpeed, maxShutterSpeed);
>> -		double stepGain = std::clamp(exposureValue / shutterTime,
>> -					     kMinGain, kMaxGain);
>> -		LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
>> -				    << shutterTime << " and "
>> -				    << stepGain;
>> +	utils::Duration exposureValue = filteredExposure_;
>> +	utils::Duration shutterTime = minShutterSpeed;
>>   
>> -		exposure = shutterTime / lineDuration_;
>> -		analogueGain = stepGain;
>> +	/*
>> +	* Push the shutter time up to the maximum first, and only then
>> +	* increase the gain.
>> +	*/
>> +	shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
>> +						  minShutterSpeed, maxShutterSpeed);
>> +	double stepGain = std::clamp(exposureValue / shutterTime,
>> +				     kMinGain, kMaxGain);
>> +	LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
>> +			    << shutterTime << " and "
>> +			    << stepGain;
>> +
>> +	exposure = shutterTime / lineDuration_;
>> +	analogueGain = stepGain;
>> +
>> +	/*
>> +	 * Update the exposure value for the next process call.
>> +	 *
>> +	 * \todo Obtain the values of the exposure time and analog gain
>> +	 * that were actually used by the sensor, either from embedded
>> +	 * data when available, or from the delayed controls
>> +	 * infrastructure in case a slow down caused a mismatch.
>> +	 */
>> +	prevExposureValue_ = shutterTime * analogueGain;
>>   
>> -		/*
>> -		 * Update the exposure value for the next process call.
>> -		 *
>> -		 * \todo Obtain the values of the exposure time and analog gain
>> -		 * that were actually used by the sensor, either from embedded
>> -		 * data when available, or from the delayed controls
>> -		 * infrastructure in case a slow down caused a mismatch.
>> -		 */
>> -		prevExposureValue_ = shutterTime * analogueGain;
>> -	}
>>   	lastFrame_ = frameCount_;
> 
> This is a functional change, with no mention of it (and no explanation
> of why it's correct) in the commit message.

Mmmh, if is "just" about removing one else and a LOG() message... I 'm 
failing to see the functional change here...

> 
>>   }
>>   
>