  Single Image Super Resolution (SISR) techniques based on Super Resolution
Convolutional Neural Networks (SRCNN) are applied to micro-computed tomography
({\mu}CT) images of sandstone and carbonate rocks. Digital rock imaging is
limited by the capability of the scanning device resulting in trade-offs
between resolution and field of view, and super resolution methods tested in
this study aim to compensate for these limits. SRCNN models SR-Resnet, Enhanced
Deep SR (EDSR), and Wide-Activation Deep SR (WDSR) are used on the Digital Rock
Super Resolution 1 (DRSRD1) Dataset of 4x downsampled images, comprising of
2000 high resolution (800x800) raw micro-CT images of Bentheimer sandstone and
Estaillades carbonate. The trained models are applied to the validation and
test data within the dataset and show a 3-5 dB rise in image quality compared
to bicubic interpolation, with all tested models performing within a 0.1 dB
range. Difference maps indicate that edge sharpness is completely recovered in
images within the scope of the trained model, with only high frequency noise
related detail loss. We find that aside from generation of high-resolution
images, a beneficial side effect of super resolution methods applied to
synthetically downgraded images is the removal of image noise while recovering
edgewise sharpness which is beneficial for the segmentation process. The model
is also tested against real low-resolution images of Bentheimer rock with image
augmentation to account for natural noise and blur. The SRCNN method is shown
to act as a preconditioner for image segmentation under these circumstances
which naturally leads to further future development and training of models that
segment an image directly. Image restoration by SRCNN on the rock images is of
significantly higher quality than traditional methods and suggests SRCNN
methods are a viable processing step in a digital rock workflow.
