1. An image upsampling system, comprising: at least one first convolutional network and at least one muxer layer that are cascaded; wherein an signal input end of the image upsampling system is connected with a signal input end of a first convolutional network in the at least one first convolutional network, and a signal output end of the image upsampling system is connected with a signal output end of a last muxer layer in the at least one muxer layer; a signal input end of every muxer layer in the at least one muxer layer is connected with a signal output end of a first convolutional network located in a stage prior to the muxer layer in the at least one first convolutional network, or connected with a signal output end of another muxer layer located in a stage prior to the muxer layer in the at least one muxer layer; the first convolutional network is configured for converting an image input to its signal input end into a plurality of feature images and outputting the feature images to the signal input end of the muxer layer connected therewith; the muxer layer is configured for synthesizing every n×n feature images in the feature images input to its signal input end into a feature image whose resolution is n×n times that of the input feature image and outputting the same; and a number of feature images input to the muxer layer is a multiple of n×n, n being an integer greater than one.