关键词: 图像水印, 分形压缩, 正交分形编码, 拼贴误差

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