histogram before and after creating an image

I am trying to get histograms from certain parts of an image. My procedure is as below 1. I have an image (say image1) and I am cropping out a bit of that image as crop1 using imcrop

2. crop 1 is just an array and I am taking a histogram of that array and it gives me a distribution (Gaussian in my case)

3. Now I save the cropped part as .bmp file

4. next I read (imread) the bmp and redraw the histogram and I cannot recreate the distribution at all.

Is there something in the process of creating an image file ? I would like to be able to get the histogram without having to crop every time? can there be a work around?