What are "VGG54" and "VGG22" derived from the VGG19 CNN?
Reading the article, it seems like they define VGG54 as the loss calculated from the euclidean distance between the $\phi_{5,4}$ feature maps derived from both the high and low resolution images using the VGG19 network. Where $\phi_{i,j}$ is defined as "the feature map obtained by the j-th convolution (after activation) and before the i-th max-pooling layer within the VGG19 network".