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

[Kieran Bingham]

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/[/(/

> 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>

> +	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