Discrete Cosine Transform Coding Research Articles

Adaptive transform coding incorporating Time Domain Aliasing Cancellation

Adaptive transform coding incorporating Time Domain Aliasing Cancellation (TDAC) is presented in this paper for speech coding at low data rates. The TDAC transform differs from the conventional Discrete Cosine Transform (DCT) in that the analysis/synthesis window length can be longer than the system decimation factor. The channel bandwidth of the TDAC transform is narrower when compared to the DCT and therefore results in less spectral interaction occurring between bands. The TDAC transform coder employs forward adaptive scalar quantization of the transform coefficients and dynamic bit allocation over a block time corresponding to three transform operations. The associated side information is vector quantized, resulting in a side information overhead of 1.625 K bits per second. Both subjective and objective comparisons were made between TDAC and DCT coders at data rates of 9.6 K, 12 K and 16 K bits per second. The objective comparison involved segmental signal to noise ratio (SNRSEG) measurements while the subjective quality assessment was determined from A-B comparisons of recovered speech passed through the TDAC coder, the DCT coder and log PCM coders. The results indicate the TDAC transform coder is both objectively and subjectively superior to a transform coder employing the conventional DCT.

Improvements of Transform Coding Algorithm for Motion-Compensated Interframe Prediction Errors-DCT/SQ Coding

A new hybrid coding method for transmitting videoconferencing images at a bit rate 384 kbits/s is proposed. Considering the characteristics of motion-compensated interframe prediction errors for typical videoconferencing scenes, a filter is introduced to separate pulsive components on which conventional discrete cosine transform (DCT) coding method does not work well. These separated pulsive components are coded by using scalar quantization (SQ). The remainder are DCT coded. For DCT coefficients, an adaptive coding method based on the classification of DCT coefficients is applied in order to improve the coding performance. Since the proposed method employs both DCT coding and SQ of prediction errors, it is named "DCT/SQ coding method." Experimental results show that the DCT/SQ coding method is effective to reduce so-called mosquito effects, and thus it can improve the quality of decoded images.

Discrete Cosine Transform Coding for TV Signal

An efficient encoding technique using discrete cosine transform (DCT) for bandwidth compression is described. Real-time one-dimensional DCT has been developed by maintaining a balance between complexity of implementation and performance. Excellent performance is demonstrated in terms of subjective quality.

Distributions of the Two-Dimensional DCT Coefficients for Images

For a two-dimensional discrete cosine transform (DCT) image coding system, there have been different assumptions concerning the distributions of the transform coefficients. This paper presents results of distribution tests that indicate that for many images the statistics of the coefficients are best approximated by a Gaussian distribution for the DC coefficient and a Laplacian distribution for the other coefficients. Furthermore, from a simulation of the DCT coding System it is shown that the assumption that the coefficients are Laplacian yields a higher actual output signal-to-noise ratio and a much better agreement between theory and simulation than the Gaussian assumption.