自然界中存在大量的纹理，往往具有自相似性，即一小块纹理就能反映整体纹理的特点。先有一个小的纹理图像,然后合成一个大的。-The presence of large amounts of grain in the nature, often with self-similarity, namely a small piece of texture can reflect the overall characteristic. There is a small texture image first, and then a big synthesis.