What does torchvision.transforms.Resize(size, interpolation=2) actually do?
Does it add to the image if too small or crop if too big or just stretch the image to the desired size?

When you set interpolation=2, then you are using Bilinear interpolation, ti can be either used for upsampling or down sampling. In the case of upsampling you are doing something like 

There are several types of upsampling and down-sampling, but bilinear one uses a combination of the neighbouring pixels to cimpute the new pixel.

Look to this links for more informations: link1; link2
