Images are not padded

[Praveen94]

I was working on the Severstal Steel Defect Detection competition.When seeing the visualizations in Tensorboard using the GradCAMCallback I was not able to easily distinguish each of the images.

I was able to easily distinguish each of the images when they are padded like so.

[RaphaelMeudec]

Thanks for raising this, I'll look into it. I'm not sure if padding will be the final solution, but visualization can definitely be improved