Abstract: A watermarking algorithm proposed by Pi et al is improved in order to embed a binary copyright symbol into a host image.In detail，the host image is first divided into non-overlapping range blocks of fixed size，which are encoded by fractal coding（using orthogonal fractal coding method）.The range blocks are then sorted by collage errors to become a descending range sequence.The range sequence is partitioned into three subsequences according to the content of the host image.Next，the watermark，which is first scrambled using Arnold transform，is embedded into the quantized means of distinct range blocks in the three range subsequences by a new quantization-based embedding formula with different quantized steps，followed by fractal decoding.The experimental results show that this algorithm really achieves good perceptual invisibility and is also very robust against some image processing such as cropping，scribbling，adding noise，filtering，and JPEG compression.

Key words: image watermarking, fractal compression, orthogonal fractal coding, collage error

摘要： 改进了一个分形水印算法，它把二值版权图标嵌入到分形压缩的图像文件中。具体说，把宿主图像分成大小相同的不重叠的子块，对这些子块进行分形编码（采用正交分形编码方法）。这些子块按拼贴误差的大小进行降序排列，并根据宿主图像内容分成三个子列。按照新的量化嵌入公式，经Arnold变换置乱后的水印被强度不同地嵌入三个子列的子块的量化均值中，通过分形解码得到含水印图像。实验表明，该算法隐蔽性强，并对剪切、涂抹、加噪、滤波以及JPEG压缩等具有较强的鲁棒性。

关键词: 图像水印, 分形压缩, 正交分形编码, 拼贴误差