Question

I have an image. I want to display a quiver plot of the gradient image that I get using gradient function in MATLAB, preferably superimposed on the gradient image.

I = imread('image.png');
[gx,gy] = gradient(double(rgb2gray(I)));
g = abs(gx) + abs(gy);
figure;
imshow(g, []);
hold on;
quiver(abs(gx),abs(gy));

This is what I tried, and all I get is a completely blue display.

Answer 1

I think all you see is the arrows, but they’re too close together.
If you plot the two graphs (imshow(g) and quiver) separately, they show up normal. The imshow only shows the pixels without any scaling, if you fix that (make it scale) the quiver arrows also will have more space between them and become visible.
You can do just that by adding the 'InitialMagnification','fit' option to imshow:

imshow(g,'InitialMagnification','fit')

Or you can show less quiver arrows:

figure;
imshow(g, []);  % [] to display image properly     
hold on;

[Nx, Ny] = size(g);
xidx = 1:10:Nx;
yidx = 1:10:Ny;
[X,Y] = meshgrid(xidx,yidx);
quiver(Y',X',abs(gx(xidx,yidx)),abs(gy(xidx,yidx)));