[Digikam-devel] about HSL optimizations

[Julien Narboux]

Hi,

The HSL filter contains an optimisation:

http://websvn.kde.org/trunk/extragear/graphics/digikam/libs/dimg/filters/hsl/hslfilter.cpp?revision=1089024&view=markup

Instead of using the following simple algorithm :
1- convert each pixel to h,s,l 
2- then add the parameters to the different channels h+ph, s+ps, l+pl 
and clamp the values
3- convert back to rgb

The plugin precomputes all the possible values for h+ph, s+ps, l+pl 
using arrays of size 256 and 65635 and then apply the precomputed value 
to the picture.

I would like to patch this to add a vibrance tool, it means that i want 
to change the saturation depending on the hue.
This optimisation prevents me from doing that in a very simple way.

So I tried a stupid patch to remove this optimisation.
With a huge panorama of 54 mega pixels, I get 17 sec of computing time 
without the optimisation and 14sec with the optimisation.

My question is the following:
 Does it worth it ?

Julien


Here is the stupid patch: warning it is just a test for speed parameters 
are not taken into account.

Index: libs/dimg/filters/hsl/hslfilter.cpp
===================================================================
--- libs/dimg/filters/hsl/hslfilter.cpp (révision 1099970)
+++ libs/dimg/filters/hsl/hslfilter.cpp (copie de travail)
@@ -198,8 +198,16 @@
             // convert RGB to HSL
             color.getHSL(&hue, &sat, &lig);

+            //julien test
+
+            hue=CLAMP065535(hue);
+            sat=CLAMP065535(sat+1000);
+            lig=CLAMP065535(lig+1000);
+
+
             // convert HSL to RGB
-            color.setRGB(d->htransfer16[hue], d->stransfer16[sat], 
d->ltransfer16[lig], sixteenBit);
+            //color.setRGB(d->htransfer16[hue], d->stransfer16[sat], 
d->ltransfer16[lig], sixteenBit);
+            color.setRGB(hue, sat, lig, sixteenBit);

             data[2] = color.red();
             data[1] = color.green();
@@ -222,10 +230,21 @@

             // convert RGB to HSL
             color.getHSL(&hue, &sat, &lig);
-
+
+            //julien test
+            /*
+            hue=CLAMP0255(hue);
+            if (lig>128)
+            {
+               sat=CLAMP0255(sat+20);
+            }
+            lig=CLAMP0255(lig+20);
+            */
+
             // convert HSL to RGB
-            color.setRGB(d->htransfer[hue], d->stransfer[sat], 
d->ltransfer[lig], sixteenBit);
-
+             color.setRGB(d->htransfer[hue], d->stransfer[sat], 
d->ltransfer[lig], sixteenBit);
+            // color.setRGB(hue, sat, lig, sixteenBit);
+
             data[2] = color.red();
             data[1] = color.green();
             data[0] = color.blue();

Julien