The disclosure provides methods and image processing devices for image super resolution, image enhancement, and convolutional neural network (CNN) model training. The method for image super resolution includes the following steps. An original image is received, and a feature map is extracted from the original image. The original image is segmented into original patches. Each of the original patches is classified respectively into one of patch clusters according to the feature map. The original patches are processed respectively by different pre-trained CNN models according to the belonging patch clusters to obtain predicted patches. A predicted image is generated based on the predicted patches.