increased error verbosity.

Author: VendorMap

index.js

@@ -33,7 +33,7 @@ export default function pixelmatch(img1, img2, output, width, height, options =
     if (img1.length !== img2.length || (output && output.length !== img1.length))
         throw new Error('Image sizes do not match.');
 
-    if (img1.length !== width * height * 4) throw new Error('Image data size does not match width/height.');
+    if (img1.length !== width * height * 4) throw new Error('Image data size does not match width/height. Expecting ' + width * height * 4 + '. Got ' + img1.length);
 
     // check if images are identical
     const len = width * height;