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

[Kieran Bingham]

On 28/09/2021 17:32, Jean-Michel Hautbois wrote:
> 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... ?

If it's a standard mathematical definition to use in that way, that's fine.


>>>>> 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
>>>>