Add vignette filter (issue #137)

Adapter/AdapterInterface.php

@@ -252,6 +252,16 @@ public function colorize($red, $green, $blue);
      */
     public function sepia();
 
+    /**
+     * apply vignetting to the image.
+     *
+     * @param int $sharpness value in range [0, 10], smaller is sharper
+     * @param int $level value in range [0, 1], smaller is brighter
+     *
+     * @return $this
+     */
+    public function vignette($sharpness=0.5, $level=0.5);
+
     /**
      * Merge with another image.
      *

Adapter/GD.php

@@ -210,6 +210,37 @@ public function sepia()
         return $this;
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function vignette($sharpness=0.5, $level=0.5)
+    {
+
+        $width = imagesx($this->resource);
+        $height = imagesy($this->resource);
+
+        for($x = 0; $x < imagesx($this->resource); ++$x){
+            for($y = 0; $y < imagesy($this->resource); ++$y){   
+                $index = imagecolorat($this->resource, $x, $y);
+                $rgb = imagecolorsforindex($this->resource, $index);
+
+                $l = sin(M_PI / $width * $x) * sin(M_PI / $height * $y);
+                $l = pow($l, $sharpness);
+                $l = 1 - $level * (1 - $l);
+
+                $rgb['red'] *= $l;
+                $rgb['green'] *= $l;
+                $rgb['blue'] *= $l;
+
+                $color = imagecolorallocate($this->resource, $rgb['red'], $rgb['green'], $rgb['blue']);
+
+                imagesetpixel($this->resource, $x, $y, $color);   
+            }
+        }
+
+        return $this;
+    }
+
     /**
      * {@inheritdoc}
      */

Adapter/Imagick.php

@@ -208,6 +208,19 @@ public function sepia()
         // TODO: Implement sepia() method.
     }
 
+    /**
+     * apply vignetting to the image.
+     *
+     * @param int $sharpness value in range [0, 10], smaller is sharper
+     * @param int $level value in range [0, 1], smaller is brighter
+     *
+     * @return $this
+     */
+    public function vignette($sharpness=0.5, $level=0.5)
+    {
+        // TODO: Implement vignette() method.
+    }
+
     /**
      * Merge with another image.
      *