And obviously I forgot to use my own code...

dist/preview release/babylon.max.js

@@ -51278,7 +51278,7 @@ var BABYLON;
             _this._cameraToneMappingEnabled = true;
             _this._updateParameters();
             _this.onApply = function (effect) {
-                var aspectRatio = _this.width / _this.height;
+                var aspectRatio = _this.aspectRatio;
                 // Color 
                 BABYLON.ColorCurves.Bind(_this.colorCurves, effect);
                 // Vignette

src/PostProcess/babylon.imageProcessingPostProcess.ts

@@ -70,7 +70,7 @@
             this._updateParameters();
 
             this.onApply = (effect: Effect) => {
-                let aspectRatio = this.width / this.height;
+                let aspectRatio = this.aspectRatio;
                 
                 // Color 
                 ColorCurves.Bind(this.colorCurves, effect);