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

[Jean-Michel Hautbois]

On 28/09/2021 18:31, Kieran Bingham wrote:
> 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.
> 
> 

Sorry about that, it is the mathematical definition, maybe should we
write it differently... ?

>>>> 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
>>>