Frequency domain measurement of blockiness in MPEG-2 coded video

Blockiness in the MPEG2 coded pictures is due to luminance discontinuities across the DCT block boundaries. Using the Sobel operators, these discontinuities can be extracted. After segmentation into smaller blocks of pixels and Fourier transformation into frequency domain, the blockiness will be translated into harmonics whose amplitude and phase can provide vital information for quantifying the blockiness. The amplitude of the harmonics is proportional to the degree of blockiness, while the phase of the harmonics can be used to verify that the harmonics are not due to contextual details in the picture. By examining both the amplitude and phase information of the harmonics, an accurate blockiness detector that needs no reference pictures has been devised, achieving a high correlation of 0.88 between the model prediction and the subjective data.