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

[Laurent Pinchart]

On Tue, Sep 28, 2021 at 05:36:24PM +0100, Kieran Bingham wrote:
> 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.

Another option is [0, 8[ which I find more readable (in particular it's
not immediately visible that (0, 8) means ]0, 8[ in my opinion), but
that may just be me.

https://en.wikipedia.org/wiki/Interval_(mathematics)#Including_or_excluding_endpoints

> >>>>> 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. */

	/*Hardcode the green gain to 1.0. */

> >>>>>  	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 */

Looks good to me.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> >>>> 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)...:

Sometime indeed :-)

> >>>> 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;
> >>>>>  

-- 
Regards,

Laurent Pinchart