Decoding method and device for JPEG image

The invention applies to the image processing field, and provides a decoding method for a JPEG image and a decoding device for the JPEG image. The method comprises the following steps: obtaining the header information of an original image, wherein the header information includes the width information, the height information and the code table information of the original image; decoding a minimum coding unit of the original image according to the information entropy of the code table, and processing a data block contained in the minimum coding unit; determining a reduction mode and a reduction coefficient of the image according to the width information of the original image, the height information of the original image and the size of a screen for outputting the target image; carrying out an inverse discrete cosine transform to the data selected from the data block according to the reduction mode and the reduction coefficient of the image; and generating the target image based on the data block undergoing the inverse discrete oscine transform. By using the method and device for JPEG image decoding provided by embodiment of the invention, the data in IDCT calculation under high complexity can be reduced and without increasing the cost; the efficiency on decoding the JPEG image can be effectively improved; and the internal memory can be saved as well.