issue with imshow ploting

I am trying to plot/show an image with the certain parameters, but it doesn't show. Only the contour. Does anyone know how I can resolve my image to be shown the the parameters and contour? Thanks in advance

    imshow(image,'Border','tight','InitialMagnification',100)
    colormap(gray)
    hold on

    contour(phi,[0 0],'r')

Answer 1

[Brian B]

It is probably a scaling issue. What are the sizes of image and phi?

[Brian B]

If I use

 image = rand(100,140);
 [X,Y] = meshgrid(1:140);
 phi = cos(X/5).*sin(Y/4);

then I can see the contour on top of the image with your code.

[Jerome]

image and phi are the same size, 700 x 900

[Brian B]

Do you see the image after the first statement (before you change the colormap and plot the contour)?

[Jerome]

The image never shows!

[Brian B]

What is the result of

 min(image(:))
 max(image(:))

[Brian B]

...or just try

imshow(image,[],'Border','tight','InitialMagnification',100)

(note the empty brackets).

[Jerome]

 min(image(:)) - 7
 max(image(:)) = 255

[Brian B]

By default, imshow expects values between 0 and 1. You can normalize your matrix, or you can explicitly tell it what range to map to the coloraxis (using 'DisplayRange' or the bracket notation above, but with the min and max values as in [-7 255]), or you can tell it to map the whole range by passing in the empty brackets as I did above.

[Jerome]

Thanks a lot!

Answer 2

[Image Analyst]

It's not clear if you meant

min(image(:)) = 7

or

min(image(:)) = -7

But either way you can do

imshow(yourImage, []);

It's also a bad idea to call your image "image" because it would blow away the built in image() function. I hope you didn't do that.

[Brian B]

True! I read it so quickly I didn't even notice the missing "=".

On the same note, as a control engineer I am always appalled when examples in the MATLAB documentation assign the output of a function testing some true or false condition to a variable named tf! Where are your transfer functions, now?