Histogram analysis of JPEG compressed images as an aid in image deblocking

Abstract

Summary form only given, substantially as follows. Transform coded images suffer from specific image degradations. In the case of standard JPEG compression/decompression the image quality losses are known to be blocking effects resulting from mean value discontinuities along the 8*8 pixel block boundaries as well as ringing artifacts due to the limited precision of the reconstruction from linear combinations of quantized or discarded basis functions. The most evident consequence of JPEG compression is the fragmentation of image histograms mainly caused by blocking in low activity image subareas. The histogram of the image shows spikes that contain most of the signal amplitudes, the other values are distributed on the remaining permissible levels. As a measure of the blocking effect, the blocking factor is defined as the ratio of the spikes area to the total area of image histogram. This method represents a promising approach to the control of locally adaptive image deblocking when the necessary enhancement depends on the local image characteristics. The blocking factor is easy to compute and provides a direct measure of the local image degradation due to blocking. A new deblocking algorithm is proposed.