How to get back the original image?

If let say I have an image I(x,y), and then it is transformed into a phase function as: I2(x,y)=exp(i*pi*I(x,y)); then how can I get back the image I(x,y) from I2(x,y)?

Answer 1

[Thorsten]

 I = rand(10); % sample data
 I2 = exp(1i*pi*I);
 I1 = real(log(I2)/pi/1i);

[RAVI KUMAR]

First of all, Thank you sir but its okay with random numbers; the problem is if we use a gray scale image (for example "lena.jpg") it will not give the result.

[Thorsten]

Why not?

I tested with

 I = im2double(imread('cameraman.tif'));

and it worked fine.