[Digikam-devel] Re: RFC, fix overexposing white balance

[Gilles Caulier]

Thanks Giuliano for you patch.

Please file a bug in KDE bugzilla system and attach your patch. We
will review later. Look here for details :

http://www.digikam.org/drupal/contrib

It's always better to use bugzilla instead to post on maillist. We use
Bugzilla file ID for AQ stuff. It's the real story of the project.
It's difficult to link source code to a mailing list post.

Also, take a care to use code from svn trunk to create patch.

Thanks in advance

Gilles Caulier



2010/12/6 Giuliano Pochini <pochini at shiny.it>:
> Hi all!
>
> IMHO the white balance tool is quite useless in its current form because it
> overexposes and clips at least one of the rgb components almost always. The
> exposure compensation thing does not help because it is applied on the
> already clipped image. I wrote the simple patch below that makes the wb
> tool useable by scaling down the wb multipiers just enough to prevent
> clipping.
>
> The biggest problem is that the final result can be quite a lot dimmer than
> the preview image because the scaler smooths the (usually tiny) brightest
> spots of the photo.
>
>
>
> --- digikam-1.6.0/libs/dimg/filters/wb/wbfilter.cpp__orig       2010-11-22 18:47:36.000000000 +0100
> +++ digikam-1.6.0/libs/dimg/filters/wb/wbfilter.cpp     2010-12-06 22:37:29.000000000 +0100
> @@ -294,6 +294,38 @@ void WBFilter::adjustWhiteBalance(uchar*
>         uchar  red, green, blue;
>         uchar* ptr = data;
>
> +
> +        int maxr, maxg, maxb, max;
> +        double adjust;
> +
> +        // Look for the maximum r, g, b values in the given image
> +        maxr = maxg = maxb = 0;
> +        for (j = 0 ; j < size; ++j) {
> +            if (maxb < ptr[0])  maxb = ptr[0];
> +            if (maxg < ptr[1])  maxg = ptr[1];
> +            if (maxr < ptr[2])  maxr = ptr[2];
> +            ptr += 4;
> +        }
> +printf("maxrgb=%d, %d, %d\n", maxr, maxg, maxb);
> +printf("mrgb=%f, %f, %f\n", d->mr, d->mg, d->mb);
> +        // White balance them and find the most overexposed one
> +        maxr *= d->mr;
> +        maxg *= d->mg;
> +        maxb *= d->mb;
> +        max = qMax(maxb, maxg);
> +        max = qMax(max, maxr);
> +printf("m*maxrgb=%d, %d, %d  m*max=%d clamp_at=%d\n", maxr, maxg, maxb, max, d->rgbMax-1);
> +        // Scale wb coefficients down if needed
> +        if (max > d->rgbMax-1) {
> +            adjust = (double)(d->rgbMax-1) / max;
> +printf("adjust=%f\n", adjust);
> +            d->mb = d->mb * adjust;            // Overwrites d->mx !!
> +            d->mg = d->mg * adjust;
> +            d->mr = d->mr * adjust;
> +        }
> +        ptr = data;
> +
> +
>         for (j = 0 ; runningFlag() && (j < size) ; ++j)
>         {
>             int v, rv[3];
>
>
>
>
> --
> Giuliano.
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