Shapiro的零树编码方法是众多小波图象编码方法中的佼佼者，但通过研究发现，图象的小波系数经过量化和零树编码后，如果按一定的顺序扫描，则零树根会连续出现，因此，若对Shapiro的零树编码方法进行改进，即在零树编码之后，熵编码之前，对连续排列的零树根进行游程编码，则可以进一步提高图象编码的压缩比。理论分析和实验结果均表明，该方法可取得较好的效果。

After quantization, a lot of image's wavelet coefficients will become zero valued. How to encode the location of these zero valued coefficients with as few symbols as possible is the key to increase the compression ratio of image coding. Shapiro presented the so called zerotree structure to encode these zero valued coefficients, in which the root of a zerotree is the only symbol to be encoded. One can obtain from the root's location the locations of all zero valued coefficients within the zerotree. Shapiro's zerotree coding has been accepted by JPEG2000, a new image coding international standard. In this paper we present an improvement to Shapiro's zerotree coding. We find in practice that after quantization and zerotree coding of image's wavelet coefficients, the roots of zerotrees will appear consecutively if they are scanned following a certain order. Thus, we add the runlength coding of consecutive roots of zerotrees before entropy coding to increase the compression ratio of image coding. Theoretical analysis and experimental results presented in this paper show that our algorithm improves the performance of Shapiro's zerotree coding.