How to get the pixel value at centroid point

how i get the pixel value at the centroid of image

i did as below

cn = s(1).Centroid;
rc = round(cn);
pixelValue = img(rc(1),rc(2));

but in some cases error is shown as

Index exceeds matrix dimensions.

Error in exe_demo (line 73)
pixelValue = img(rc(1),rc(2))

But the centroid point is plotted correctly. How to get the pixel value at that point without error.

Answer 1

[Walter Roberson]

pixelValue = img(rc(2), rc(1));

The centroid coordinate order is X, Y, but image arrays are in the order Y, X.