How do you plot a line on a function defined by colors?

Hello, I want to plot a line on a color defined function (enclosed example below), such that the line follows the boarders between colors. I don't want to plot a line that roughly follows the color boarders but follows the boarder exactly based on the change in color. However, I am unsure how to acomplish this. Any help appreciated.

Example:

[Walter Roberson]

Is that a contourf() output? Or is it an imagesc() or imshow() ? or a pcolor() ?

Does the underlying data have sharp data boundaries, or is the underlying data continuous ?

[Lulu]

It is an imagesc(). The underlying data has sharp data boudaries.

[Dyuman Joshi]

Could you attach the data? Use the paperclip button to attach.

Answer 1

[KSSV]

[X,Y,Z] = peaks(100) ;
contourf(X,Y,Z)

Answer 2

[Voss]

img = imread('image.png');

imagesc(img)
hold on
contour(mean(img,3),'k')

Answer 3

[Walter Roberson]

levels = unique(YourData);
contourf(YourData, levels);