[libcamera-devel] [PATCH v2 13/13] ipa: ipu3: Use sensor limits for analogue gain

[Jean-Michel Hautbois]

Hi Laurent,

On 21/10/2021 04:39, Laurent Pinchart wrote:
> Hi Jean-Michel,
> 
> Thank you for the patch.
> 
> On Wed, Oct 20, 2021 at 05:46:07PM +0200, Jean-Michel Hautbois wrote:
>> Instead of using constants for the analogue gains limits, use the
>> minimum and maximum from the configured sensor.
>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
>> ---
>>   src/ipa/ipu3/algorithms/agc.cpp | 25 +++++++++++++------------
>>   src/ipa/ipu3/algorithms/agc.h   |  3 +++
>>   2 files changed, 16 insertions(+), 12 deletions(-)
>>
>> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
>> index fc37eca4..690ad7e6 100644
>> --- a/src/ipa/ipu3/algorithms/agc.cpp
>> +++ b/src/ipa/ipu3/algorithms/agc.cpp
>> @@ -30,10 +30,9 @@ static constexpr uint32_t kInitialFrameMinAECount = 4;
>>   /* Number of frames to wait between new gain/exposure estimations */
>>   static constexpr uint32_t kFrameSkipCount = 6;
>>   
>> -/* Maximum analogue gain value
>> - * \todo grab it from a camera helper */
>> -static constexpr double kMinGain = 1.0;
>> -static constexpr double kMaxGain = 8.0;
>> +/* Limits for analogue gain values */
>> +static constexpr double kMinAnalogueGain = 1.0;
>> +static constexpr double kMaxAnalogueGain = 16.0;
> 
> Should we keep 8.0, or is there a reason to allow gains up to 16.0 ? It
> seems like it will add lots of noise.

It is a clamp value, there is only one sensor I tested which can do more 
than 8.0 which is the ov5670 (I believe because of a broken driver). We 
could keep 8.0 indeed.

> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
>>   
>>   /* Histogram constants */
>>   static constexpr uint32_t knumHistogramBins = 256;
>> @@ -53,15 +52,17 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
>>   	lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
>>   		      / configInfo.sensorInfo.pixelRate;
>>   
>> -	/* Configure the default exposure and gain */
>> -	context.frameContext.agc.gain =
>> -		context.configuration.agc.minAnalogueGain;
>> -	context.frameContext.agc.exposure = minExposureLines_;
>> -
>>   	/* \todo replace the exposure in lines storage with time based ones */
>>   	minExposureLines_ = context.configuration.agc.minShutterSpeed / lineDuration_;
>>   	maxExposureLines_ = context.configuration.agc.maxShutterSpeed / lineDuration_;
>>   
>> +	minAnalogueGain_ = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
>> +	maxAnalogueGain_ = std::min(context.configuration.agc.maxAnalogueGain, kMaxAnalogueGain);
>> +
>> +	/* Configure the default exposure and gain */
>> +	context.frameContext.agc.gain = minAnalogueGain_;
>> +	context.frameContext.agc.exposure = minExposureLines_;
>> +
>>   	prevExposureValue_ = context.frameContext.agc.gain
>>   			   * context.frameContext.agc.exposure
>>   			   * lineDuration_;
>> @@ -139,7 +140,7 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
>>   	utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
>>   	utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
>>   
>> -	utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
>> +	utils::Duration maxTotalExposure = maxShutterSpeed * maxAnalogueGain_;
>>   	currentExposure_ = std::min(currentExposure_, maxTotalExposure);
>>   	LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
>>   			    << ", maximum is " << maxTotalExposure;
>> @@ -154,10 +155,10 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
>>   	* Push the shutter time up to the maximum first, and only then
>>   	* increase the gain.
>>   	*/
>> -	shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
>> +	shutterTime = std::clamp<utils::Duration>(exposureValue / minAnalogueGain_,
>>   						  minShutterSpeed, maxShutterSpeed);
>>   	double stepGain = std::clamp(exposureValue / shutterTime,
>> -				     kMinGain, kMaxGain);
>> +				     minAnalogueGain_, maxAnalogueGain_);
>>   	LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
>>   			    << shutterTime << " and "
>>   			    << stepGain;
>> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
>> index ad133b98..1840205b 100644
>> --- a/src/ipa/ipu3/algorithms/agc.h
>> +++ b/src/ipa/ipu3/algorithms/agc.h
>> @@ -45,6 +45,9 @@ private:
>>   	uint32_t minExposureLines_;
>>   	uint32_t maxExposureLines_;
>>   
>> +	double minAnalogueGain_;
>> +	double maxAnalogueGain_;
>> +
>>   	utils::Duration filteredExposure_;
>>   	utils::Duration currentExposure_;
>>   	utils::Duration prevExposureValue_;
>