How do I add a grid over this image?

I'm wanting to add a 10x10 grid over the image in the figure below. I produced this density plot using image(), but wish to add an outline to each small square. I have seen examples of how to add a grid over an image, but this involves modifying columns and rows of pixels and setting their colour to black, however, since each small square in my figure is a pixel, this doesnt work. Any help/suggestions anyone may have would be greatly appreciated.

Thanks

Answer 1

[Image Analyst]

Try line:

[rows, columns, numberOfColorChannels] = size(rgbImage);
hold on;
for row = 10:10:rows
        line([1, columns], [row, row], 'Color', 'r');
end
for col = 10:10:columns
        line([col, col], [1, rows], 'Color', 'r');
end