more new ideas

circle.go

@@ -11,7 +11,7 @@ type Circle struct {
 	R int
 }
 
-func (c Circle) ColorModel() color.Model { return color.AlphaModel }
+func (c Circle) ColorModel() color.Model { return color.Alpha16Model }
 func (c Circle) Bounds() image.Rectangle {
 	return image.Rect(c.Point.X-c.R, c.Point.Y-c.R, c.Point.X+c.R, c.Point.Y+c.R)
 }