Unable to write images of type 'double'

I have obtained Fourier spectrum of an image and want to save the result image into the folder as specified in my code.

but as result image is of type "double",i am unable save it.i am getting blank image at the given folder. what should i do?

Here is my code

      clc;
      clear all;
      close all;
      i=imread('D:\pendrive\test1.jpg');
      i=rgb2gray(i);
      subplot(2,2,1),imshow(i);title('Test Image');

      f=fftn(i);
      magnitude=abs(f);
      phase=angle(f);

      f1=log(1+fftshift(f));
      subplot(2,2,2),imshow(f1,[]);title('Fourier spectrum');
      a=strcat('C:\Users\Public\Pictures\Sample Pictures\results\Fourier spectrum\','.jpg');
      imwrite(f1,a);

Answer 1

[Image Analyst]

Use save() to save it as a .mat file instead of a standard uint8 image file.