DC coefficient restoration using nonlinear criterion and AC coefficients restoration

The DC coefficient restoration scheme is a technique which can be used to increase the compression ability of transform image coding by not transmitting the DC coefficients but estimating them from the transmitted AC component. We have previously proposed a nonlinear estimation criterion using the maximum a posterior (MAP) estimation technique which preserves the discontinuities during the DC coefficients restoration and solves the blocking effect in the restored images. However we also found that the performance of the nonlinear criterion is affected by the quantization error in the transmitted AC coefficients. In this paper, we combine the nonlinear criterion with the AC coefficient restoration technique. The new method preserves the discontinuities of the images and also reduces the blocking effect in the restored images in the present of quantization error in the AC coefficients.