A video processing method and system and a related device are disclosed, an encoder sends a method for compressing a pixel value of a video image to a decoder, the method includes a mapping between a pixel value of the video image before compression and a pixel value of the video image after the compression; compressing, by the encoder according to the method for compressing a pixel value, the pixel value of the video image to obtain a video image to be encoded; encoding, by the encoder, the video image to be encoded to obtain a video image encoded stream; and sending, by the encoder, the video image encoded stream to the decoder, the decoder receives and decodes the video image encoded stream to obtain a decoded video image, and decompresses a pixel value of the decoded video image to restore the pixel value of the video image before compression.