public void GrayscaleTest()
 {
     foreach (var a in Enumerable.Range(0, 256))
     {
         foreach (var r in Enumerable.Range(0, 256))
         {
             foreach (var g in Enumerable.Range(0, 256))
             {
                 foreach (var b in Enumerable.Range(0, 256))
                 {
                     var t = Color.FromArgb(a, r, g, b);
                     Assert.AreEqual(ImageFilters.GrayscaleFilter((uint)t.ToArgb()), GrayscaleFilter(t).ToArgb());
                 }
             }
         }
     }
 }