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

[Umang Jain]

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.
> '''


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) {