Abstract: From the view of the coding gain，this paper investigates the performance of 2-channel biorthogonal wavelet image copression system.Firstly，the polyphase matrix of biorthogonal wavelet filter bank is decomposed by lifting scheme，then lifting parameters with one variable are obtained combining the vanishing moment and normalization conditions.According to the Vaidy- anathan’s coding gain，the optimal value can be got.In the example，three 9-7 wavelets are constructed significantly.Although MIT wavelet is slightly lower than CDF 9-7 on the quality of reconstructed image，it is friendly implemented in hardware.Furthermore，its coding gain is more than the other two wavelets.This should be given consideration in the design of coder.

摘要： 从编码增益的角度，考察了双通道双正交小波图像编码系统的性能。首先，对双正交滤波器组的多相位矩阵进行提升分解，并结合消失矩和归一化条件，得到了含自由变量的提升参数。根据Vaidyanathan编码增益表达式求出编码增益的最优值。然后重点构造了三种9/7小波。尽管MIT小波的图像压缩质量略低于CDF 9/7小波，但它不仅系数简单，易于硬件实现，而且编码增益更大。这在编码器设计时具有重要实用价值。