save indexed images in MATLAB

Question

I have this image which with point curse it shows

X ,Y index RGB

the index values are important for me and I want to save this image and use it later. but when I am using

imwrite(im, 'importantIm.png' , 'png')

the created image does not have index value. here is the resulting saved image (png format);

I produce im , like below

im=zeros([1204 1204]);

with a loop add data to it.