[libcamera-devel] [PATCH 08/12] ipa: ipu3: awb: Correct the gain multipliers

[Jean-Michel Hautbois]

On 28/09/2021 17:53, Kieran Bingham wrote:
> On Thu, Sep 23, 2021 at 10:16:21AM +0200, Jean-Michel Hautbois wrote:
>> The gains have a precision u3.13, range [0, 8) which means that a gain
> 
> s/)/]/ or s/[/(/

Mmmh, I must disagree here, it is going from 0 to 7,99987793 and not 8
(all ones). So the interval is opened for 8.

> 
>> multiplier value of 1.0 is represented as a multiplication by 8192 in
>> the ImgU. Correct the gains as this was misunderstood in the first
>> place.
>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
>> ---
>>  src/ipa/ipu3/algorithms/awb.cpp | 15 ++++++---------
>>  1 file changed, 6 insertions(+), 9 deletions(-)
>>
>> diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
>> index 800d023c..8a926691 100644
>> --- a/src/ipa/ipu3/algorithms/awb.cpp
>> +++ b/src/ipa/ipu3/algorithms/awb.cpp
>> @@ -313,6 +313,7 @@ void Awb::awbGreyWorld()
>>  	/* Color temperature is not relevant in Grey world but still useful to estimate it :-) */
>>  	asyncResults_.temperatureK = estimateCCT(sumRed.R, sumRed.G, sumBlue.B);
>>  	asyncResults_.redGain = redGain;
>> +	/* Green gains should not be touched and considered 1. */
>>  	asyncResults_.greenGain = 1.0;
>>  	asyncResults_.blueGain = blueGain;
>>  }
>> @@ -376,15 +377,11 @@ void Awb::prepare(IPAContext &context, ipu3_uapi_params *params)
>>  							* params->acc_param.bnr.opt_center.x_reset;
>>  	params->acc_param.bnr.opt_center_sqr.y_sqr_reset = params->acc_param.bnr.opt_center.y_reset
>>  							* params->acc_param.bnr.opt_center.y_reset;
>> -	/*
>> -	 * Green gains should not be touched and considered 1.
>> -	 * Default is 16, so do not change it at all.
>> -	 * 4096 is the value for a gain of 1.0
>> -	 */
>> -	params->acc_param.bnr.wb_gains.gr = 16 * context.frameContext.awb.gains.green;
>> -	params->acc_param.bnr.wb_gains.r = 4096 * context.frameContext.awb.gains.red;
>> -	params->acc_param.bnr.wb_gains.b = 4096 * context.frameContext.awb.gains.blue;
>> -	params->acc_param.bnr.wb_gains.gb = 16 * context.frameContext.awb.gains.green;
>> +	/* 8192 is the multiplier for a gain of 1.0 */
> 
> I'd be a bit more explicit to say at least
> 
>   /* Convert to u3.13 Fixed point values with a base of 8192 */
> 
> But I'm not sure the '8192' is a base as such, perhaps just:
> 
>   /* Convert to u3.13 fixed point values */
> 
> Sometime I'm sure we could use C++ to make a u3_13 type or a FixedPoint
> class that handles this a bit more elegantly...
> 
> But I don't think we want to dwell on that right now.
> 
> Whatever works out best in the end (and I think we'll revist this with
> a FixedPoint type sometime)...:
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

OK, thx.

> 
>> +	params->acc_param.bnr.wb_gains.gr = 8192 * context.frameContext.awb.gains.green;
>> +	params->acc_param.bnr.wb_gains.r = 8192 * context.frameContext.awb.gains.red;
>> +	params->acc_param.bnr.wb_gains.b = 8192 * context.frameContext.awb.gains.blue;
>> +	params->acc_param.bnr.wb_gains.gb = 8192 * context.frameContext.awb.gains.green;
>>  
>>  	LOG(IPU3Awb, Debug) << "Color temperature estimated: " << asyncResults_.temperatureK;
>>  
>> -- 
>> 2.30.2
>>
> 
> --
> Kieran
>