A random grid based non-expanded visual cryptography scheme used to generate meaningful as well as meaningless shares. First, analyze the distribution of pixels on the share image and stack image. A probability allocation method is introduced which is capable of producing the better visual quality in share image and stack image. With this method, it not only hide the secret image by using different cover images, but also visual quality of images is improve as needed. The important part is improvement of contrast of both secret and stack images to their theoretical maximum. This method is superior to past methods for visual secret sharing.