diff --git a/index.html b/index.html
index ed90286..df843df 100644
--- a/index.html
+++ b/index.html
@@ -23,7 +23,7 @@
     <script type="text/javascript" src="scripts/modules/filter.js"></script>
     <script type="text/javascript" src="scripts/modules/filter.saturation.js"></script>
     <script type="text/javascript" src="scripts/modules/filter.chromatic.js"></script>
-    <script type="text/javascript" src="scripts/modules/filter.invert.js"></script>
+    <script type="text/javascript" src="scripts/modules/filter.offset.js"></script>
     <script type="text/javascript" src="scripts/modules/filter.eval.js"></script>
     <script type="text/javascript" src="scripts/modules/filter.balance.js"></script>
     
diff --git a/scripts/modules/filter.invert.js b/scripts/modules/filter.invert.js
deleted file mode 100644
index c9c6936..0000000
--- a/scripts/modules/filter.invert.js
+++ /dev/null
@@ -1,11 +0,0 @@
-Filter.prototype.filter_invert = function(pixels = this.pixels(),p = null)
-{
-  var d = pixels.data;
-  for (var i=0; i<d.length; i+=4) {
-      for (var j=0; j<3; j++) {
-          d[i+j] = 255 - d[i+j];
-      }
-  }
-	ronin.canvas.clear();
-	ronin.canvas.context().putImageData(pixels, 0, 0, 0, 0, pixels.width, pixels.height);
-}
diff --git a/scripts/modules/filter.js b/scripts/modules/filter.js
index e899493..a55bfcf 100644
--- a/scripts/modules/filter.js
+++ b/scripts/modules/filter.js
@@ -19,8 +19,9 @@ function Filter(element)
       case "chromatic":
         this.filter_chromatic(this.pixels(),p);
         break;
-      case "invert":
-        this.filter_invert(this.pixels(),p);
+      case "offset":
+        this.filter_offset(this.pixels(),p);
+        break;
       case "eval":
         this.filter_eval(this.pixels(),p);
         break;
diff --git a/scripts/modules/filter.offset.js b/scripts/modules/filter.offset.js
new file mode 100644
index 0000000..73f21a5
--- /dev/null
+++ b/scripts/modules/filter.offset.js
@@ -0,0 +1,19 @@
+Filter.prototype.filter_offset = function(pixels = this.pixels(),p = null)
+{
+  var v = 255; // defaults to 255 if no parameter specified
+  if (p.length > 0 && p[0]) {
+      v = parseInt(p[0]);
+      // permissible range is 0 <= v <= 255
+      if (v > 255) { v = 255;} 
+      if (v < 0) { v = 0;}
+  }
+  var d = pixels.data;
+
+  for (var i=0; i<d.length; i+=4) {
+      for (var j=0; j<3; j++) {
+          d[i+j] = v - d[i+j];
+      }
+  }
+	ronin.canvas.clear();
+	ronin.canvas.context().putImageData(pixels, 0, 0, 0, 0, pixels.width, pixels.height);
+}