Image Super-Resolution via Generative Adversarial Network Using an Orthogonal Projection

In this paper, we propose a simple but powerful idea to improve super-resolution (SR) methods based on convolutional neural networks (CNNs). We consider a linear manifold, which is the set of all SR images whose downsampling results are the same as the input image, and apply the orthogonal projection onto this linear manifold in the output layers of the CNNs. The proposed method can guarantee the consistency between the SR image and the input image and reduce the mean squared error. The proposed method is especially effective for SR methods based on generative adversarial networks (GANs), composed of one generator and one discriminator, since the generator can learn high-frequency components while maintaining low-frequency ones. Experiments show the effectiveness of the proposed technique for a GAN-based SR method. Finally we introduce an idea of extension to noisy images.