Rounding of improved DCT transform coding for H.266/VVC

Many video encoders use DCT transform coding to compress the encoded video. For hardware implementation, DCT will be approximately an integer matrix, which may cause some deviations in this process, and these deviations will accumulate and become obvious in the larger code unit. Our method is to construct all DCT-related discrete orthogonal transforms in the required size (corresponding to the coding unit supported by H.266/VVC). By using a novel discrete orthogonal matrix generation method with determined DCT-II roots, and scaling and rounding a regular DCT that depends on the quantization parameter, instead of integer approximation. We can obtain an accurate integer DCT matrix. Experimental results show that this method can not only improve the video quality and also require fewer bit rates.