diff --git a/readme.md b/readme.md
index 8378c88..e0b51d0 100644
--- a/readme.md
+++ b/readme.md
@@ -46,7 +46,7 @@ try {
 - Reads and writes files, data URIs, and image strings.
 - Manipulation: crop, resize, overlay/watermark, adding TTF text
 - Drawing: arc, border, dot, ellipse, line, polygon, rectangle, rounded rectangle
-- Filters: blur, brighten, colorize, contrast, darken, desaturate, edge detect, emboss, invert, pixelate, sepia, sharpen, sketch
+- Filters: blur, brighten, colorize, contrast, darken, desaturate, edge detect, emboss, invert, opacity, pixelate, sepia, sharpen, sketch
 - Utilities: color adjustment, darken/lighten color, extract colors
 - Properties: exif data, height/width, mime type, orientation
 - Color arguments can be passed in as any CSS color (e.g. `LightBlue`), a hex color, or an RGB(A) array.
@@ -542,6 +542,14 @@ Inverts the image's colors.
 
 Returns a SimpleImage object.
 
+#### `opacity()`
+
+Changes the image's opacity level.
+
+- `$opacity`* (float) - The desired opacity level (0 - 1).
+
+Returns a SimpleImage object.
+
 #### `pixelate($size)`
 
 Applies the pixelate filter.
diff --git a/src/claviska/SimpleImage.php b/src/claviska/SimpleImage.php
index 503edd2..c646dc9 100644
--- a/src/claviska/SimpleImage.php
+++ b/src/claviska/SimpleImage.php
@@ -1431,6 +1431,32 @@ public function invert() {
     return $this;
   }
 
+  //
+  // Changes the image's opacity level.
+  //
+  //  $opacity* (float) - The desired opacity level (0 - 1).
+  //
+  // Returns a SimpleImage object.
+  //
+  public function opacity($opacity) {
+    // Create a transparent image
+    $newImage = new SimpleImage();
+    $newImage->fromNew($this->getWidth(), $this->getHeight());
+
+    // Copy the current image (with opacity) onto the transparent image
+    self::imageCopyMergeAlpha(
+      $newImage->image,
+      $this->image,
+      $x, $y,
+      0, 0,
+      $this->getWidth(),
+      $this->getHeight(),
+      self::keepWithin($opacity, 0, 1) * 100
+    );
+
+    return $this;
+  }
+
   //
   // Applies the pixelate filter.
   //