Blocking artifact removal based on blockiness estimation
Qinggang Zhou, Chris Basoglu, Woobin Lee · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2000
We present a fast and robust blocking artifact removal method for images coded using block transforms. While other artifact removal methods apply complicated smoothing schemes on the entire image, this method estimates the level of blockiness and applies a simple low-pass filter only on the blocking artifacts. In this paper, we first formulate a function that describes the relative gradient continuities of the pixel values. This function makes use of the characteristics of the blocking artifact, such as the position and magnitude of the artifact, to distinguish real edges from the blockiness. The function is mostly continuous in smooth areas but discontinuous in blocky areas. The results of the function are compared to an empirically obtained threshold to determine the existence of a blocking artifact. Once the artifact is detected, any smoothing method can be applied. On test images coded with the JPEG standard, our method visually removed almost all of the blocking artifacts. The signal-to-noise also improved, but more importantly, the subjective quality of the images processed with our method was noticeably better than that of other methods. In addition, our method did not degrade the image areas where artifacts were not present. The false detection rate of our method was found to be less than 1% on the test images, thereby preserving the true edges in the image.