added invert method

README.md

@@ -56,6 +56,7 @@ Add the facade of this package to the `$aliases` array.
 * Image::contrast - Changes contrast of current image (-100 = min contrast, 0 = no change, +100 = max contrast)
 * Image::pixelate - Pixelate current image
 * Image::greyscale - Turn current image into a greyscale version
+* Image::invert - Invert colors of current image
 * Image::text - Write text in current image
 * Image::fill - Fill image with given color at position x,y
 * Image::rectangle - Draw rectangle in current image starting at point 1 and ending at point 2

src/Intervention/Image/Image.php

@@ -626,6 +626,18 @@ class Image
         return $this;
     }
 
+    /**
+     * Invert colors of current image
+     * 
+     * @return Image
+     */
+    public function invert()
+    {
+        imagefilter($this->resource, IMG_FILTER_NEGATE);
+
+        return $this;
+    }
+
     /**
      * Reset to original image resource
      *

tests/ImageTest.php

@@ -205,6 +205,14 @@ class ImageTest extends PHPUnit_Framework_Testcase
         $this->assertInstanceOf('Intervention\Image\Image', $img);
     }
 
+    public function testInvertImage()
+    {
+        $img = $this->getTestImage();
+        $img->invert();
+        $this->assertInstanceOf('Intervention\Image\Image', $img);
+        $this->assertEquals('#000000', $img->pickColor(0, 0, 'hex'));
+    }
+
     public function testFillImage()
     {
         $img = $this->getTestImage();