Description: This paper mainly introduces the coding and decoding process of JPEG. The coding part of the program can encode a BMP image in JEPG and compress it into a binary saved file. The image can be decompressed by the corresponding decoder program. In the process of image transmission, we often use JPEG format to encode static images. JPEG basic system is a lossy code, unable to fully recover the original image, the information has a certain loss, called lossy compression. Although we hope to be able to get a lossless compression, the compression ratio of lossy compression usually (namely the number of bytes of the original image and the image of the ratio of the number of bytes after compression, the compression ratio, the greater the compression efficiency is higher) than lossless compression. JPEG coding first converts the image color RBG into brightness Y and chroma Cr and Cb. It USES the characteristics of people's vision to be insensitive to chroma, and reduces some chromaticity data to achieve compression. JPEG takes a variety of encoding methods, including Run Length Coding and Huffman Coding, with a high compression ratio. Before coding, the data is divided into blocks, discrete cosine transform (DCT) and quantization, the low-frequency signal with large energy is retained, and the high frequency signal is discarded to achieve compression. When decoding, entropy decoding, anti-quantification, anti-discrete cosine transform (IDCT) are performed.
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