Hello all, this is the definition of total variation loss

So, I implemented it as follows:

```
def compute_total_variation_loss(img, weight):
tv_h = ((img[:,:,1:,:] - img[:,:,:-1,:]).pow(2)).sum()
tv_w = ((img[:,:,:,1:] - img[:,:,:,:-1]).pow(2)).sum()
return weight * (tv_h + tv_w)
```

Is it correct? What does it means `img[:,:,1:,:] - img[:,:,:-1,:]`

?