Have a floorplan picture I want to plot time spent per area for a day as a heatmap

I have a picture of a floor plan, that is sectioned off into a 3x3 grid. I also have time spent in each grid zone (1-9) for a day for 4 people. I want to plot this as a heatmap/frequency type plot (3D or 2d whichever looks better) and overlay that data on the image. How do I go about this? I was thinking it would be cool to color the image as the heatmap but that might be more complicated than matlab can do.