Adaptive thresholding for noisy MPEG-4 still texture image

We show that when using the MPEG-4 still image codec to compress a noisy image, increasing the compression ratio does not necessarily imply reducing the peak-signal-to-noise ratio (PSNR) of the decoded image. An optimal operating point is noted where the peak PSNR can be obtained within the low bit rate region. Yet, the visual quality of the decoded noisy images in this region is greatly degraded by the so-called “cross” shape artefact. To deal with this problem, we analyze the cause of the optimal operating point and the “cross” shape artefact when using the MPEG-4 still image codec for coding noisy images. We then propose an adaptive thresholding technique to remove the “cross” shape artefact. An analytical study is performed for the selection and validation of the threshold value used. It is shown that, by using the proposed technique, the visual quality and PSNR of the decoded images are much improved compared with the traditional MPEG-4 still image codec in coding noisy images