VanillaGrad, SmoothGrad, etc. have crosshatching

[rijobro]

Describe the bug
We've noticed that VanillaGrad and its derivatives seem to generate a crosshatching effect. It's hard to notice in the cats and dogs example (possibly because images are higher spatial resolution), but is more obvious in a 2d brain tumour classification tutorial and in @trinhdhk's research (screenshots of both below).

I think we need to update the covid and lung lesion tutorials to check if the problem persists there. As previously mentioned, it might depend on spatial resolution.

Trinh's research

2D Brain tumour detection

Expected behavior
No crosshatching.

[rijobro]

CC @ericspod

[vikashg]

closing because of inactivity