H.264 video compression principle
From an information theory point of view, an image is a source of information, and the data describing the source is the sum of the amount of information (source entropy) and the amount of information redundancy. There are many kinds of information redundancy, such as spatial redundancy, temporal redundancy, structural redundancy, knowledge redundancy, visual redundancy, etc. Data compression essentially reduces these redundancy. It can be seen that the reduction of redundancy can reduce the amount of data without reducing the amount of information of the source. Mathematically speaking, the image can be regarded as a multi-dimensional function, and the compression of the amount of data describing this function is to reduce its correlation.
According to the elements of image information, H.264 uses intra prediction, inter prediction, motion estimation and motion compensation, integer transformation, etc. to improve the compression rate of the image. Intra-frame prediction is based on the possible similarity of adjacent pixels in the image, H.264 uses the correlation of the adjacent pixels, adopts a new intra-prediction mode, through the left and upper pixels of the current pixel block Pixels) for prediction, only the difference between the actual value and the predicted value is encoded, so that the number of bits of the intra-coded pixel block can be expressed with a smaller number of bits; and inter prediction uses multi-frame reference and a smaller motion prediction area And other methods to accurately predict the next frame, thereby reducing the amount of data transmitted and reducing the temporal correlation of the image. H.264 transforms the motion estimation and intra prediction residual results from the time domain to the frequency domain, using an integer transform similar to 4 × 4 discrete cosine transform (DCT) instead of MPEG-2 and MPEG-4 In that way, a floating point conversion of 8 × 8 DCT is used. The integer-based spatial transformation has the advantages of good effect, fast calculation (only addition and shift operations are required), no adaptation problems during the inverse transformation process, and combined with the quantization process to ensure that in a 16-bit computing system, The calculation result has maximum accuracy and will not overflow. The 4 × 4 transform block is also 8 × 8 to reduce the block effect and ringing effect.
The application of H.264 standard provides technical support for the network transmission of video, especially the transmission under low bandwidth (such as wireless transmission mode). In today's explosion of information, the market requires designers to launch products faster and faster, and in order to maintain the competitiveness of products, product prices and product application features must maintain sufficient advantages, especially in the multimedia market. On the basis of providing standard algorithms, Hisilicon ’s SoC chip gives designers maximum flexibility to design suitable products, greatly reducing the manufacturer ’s input costs, shortening the time for manufacturers to launch new products, and preparing for winning the market .
Langrui Energy (Shenzhen) Co.,Ltd , https://www.langruienergy.com