[libcamera-devel] [PATCH 1/5] ipa: ipu3: agc: Drop kMaxLuminance constant

[Laurent Pinchart]

Hi Jean-Michel,

On Wed, Nov 17, 2021 at 11:09:55AM +0100, Jean-Michel Hautbois wrote:
> Hi Laurent,
> 
> Thanks for the patch !
> 
> On 16/11/2021 17:26, Laurent Pinchart wrote:
> > The kMaxLuminance constant is badly named, it's not a maximum luminance,
> > but the maximum integer value output by the AWB statistics engine for
> > per-channel averages. The constant is used in a single place, hardcoding
> > the value is actually more readable.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> I hesitated and made it a constexpr to avoid "magic values"... :-)

I also prefer avoiding magic values. Here I think "kMaxLuminance" isn't
a very good name. It's really the maximum value of the RGB averages
computed by the ImgU in AWB statistics. As it's only used in a single
function, and as I couldn't think of a good name for the constant, I
decided to drop it.

> Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> 
> > ---
> >   src/ipa/ipu3/algorithms/agc.cpp | 6 +-----
> >   1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> > index bd02c474611c..43a39ffd57d6 100644
> > --- a/src/ipa/ipu3/algorithms/agc.cpp
> > +++ b/src/ipa/ipu3/algorithms/agc.cpp
> > @@ -61,9 +61,6 @@ static constexpr double kEvGainTarget = 0.5;
> >   /* Number of frames to wait before calculating stats on minimum exposure */
> >   static constexpr uint32_t kNumStartupFrames = 10;
> >   
> > -/* Maximum luminance used for brightness normalization */
> > -static constexpr uint32_t kMaxLuminance = 255;
> > -
> >   /*
> >    * Normalized luma value target.
> >    *
> > @@ -298,8 +295,7 @@ double Agc::computeInitialY(IPAFrameContext &frameContext,
> >   		       greenSum * frameContext.awb.gains.green * .587 +
> >   		       blueSum * frameContext.awb.gains.blue * .114;
> >   
> > -	/* Return the normalized relative luminance. */
> > -	return Y_sum / (grid.height * grid.width) / kMaxLuminance;
> > +	return Y_sum / (grid.height * grid.width) / 255;
> >   }
> >   
> >   /**

-- 
Regards,

Laurent Pinchart