How can I plot parts of an image on a pcolor surface

I have a pcolor surface and also I have an image which I want to empty the black section of the image and put the reminding image on the pcolor so that the pcolor can be shown under the black section of the image and the reminding parts of the image, covers the pcolor.

my pcolor:

my image:

[KSSV]

What data you have? It can be done.

[loghman]

I have a X,Y,Z data that I use them to plot surface(with surf or pcolor) and the image.

my code:

 [x,y] = meshgrid(1:1000,1:1000);
z = x^3-sqrt(y);
I = imread('mymap.png');
imshow(I, 'InitialMag', 'fit')
hold on 
k = pcolor(x,y,z);
shading interp
colormap jet

but after plotting, the surface covers entire image hold off

Answer 1

[Image Analyst]

Set the alpha channel. Here is how to do it:

Steve Eddins's blog:

http://blogs.mathworks.com/steve/2009/02/18/image-overlay-using-transparency/

[loghman]

This is my code:

[x,y] = meshgrid(1:1000,1:1000);
z = x^3-sqrt(y);
I = imread('mymap.png');
imshow(I, 'InitialMag', 'fit')
hold on 
k = pcolor(x,y,z);
shading interp
colormap jet
hold off
set(k,'AlphaData',I)

but I get error on the last line, actually I cant control alphadata of my pcolor surface. What should I do?

[Image Analyst]

Actually I never use pcolor() since the little "boxes" don't correspond to pixels and there is one fewer row and column of boxes than there are rows and columns in your image (999 rows and 999 columns instead of 1000 rows and 1000 columns).

So if you can get an image, then use imshow() and it will work fine. Just loop over x and y and set the image at yourImage(y, x) = z. Something like

theImage = zeros(1000, 1000);
for k = 1 : length(x)
    theImage(y(k), x(k)) = z(k);
end
imshow(theImage, []);

[loghman]

actually I should use pcolor or surf because my 'z' data varies with time and in any loop I should update it.

[Image Analyst]

I don't see why that precludes using imshow(). Anyway, attach mymap.png.

[loghman]

This is image and all I want to plot a surface or pcolor under the black part of the image

[Image Analyst]

The only black part is the very thin country perimeter and the letters. Is that the part you want to show up as transparent so you can see colors through them?

[loghman]

The part that i want to be transparent is the region inside the borders of the country

[Image Analyst]

Can you provide an image where the region inside the country is black? Come on, make it easy for us to help you, not hard.

[loghman]

The link of the image that you want:

https://s16.postimg.org/wnsw1mtj9/mymap.jpg