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

[Kieran Bingham]

On 28/09/2021 16:59, Jean-Michel Hautbois wrote:
> 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.

It looks like a typo ... Is that a defined way to describe that range
otherwise? It wasn't obvious to me that you were trying to convey that
by the different symbols.


>>> 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
>>