Removing white background around image plot showing 2D matrix

I have created a image plot showing a 2D matrix. I want to append some traces onto this image plot. However, I indicated that the the trace is to be shown as markers, a white border suddenly appears between the matrix plot and the x and y axes (see attached). The only way I can make that white border disappear is if I were to remove the trace that I appended onto the image plot. How do I remove this white border while keeping the trace on the image plot?    

image plot with annoying white border No white border and no added trace

in the modify axis dialog uncheck the standoff checkbox, or execute

ModifyGraph standoff=0