I have couple of images below which I want to subtract from each other. The images are taken from the same sample at different time frames. I want to notice the movement of the particles between those time frames. So I want to take out the part of the image that only contains the liquid particles. I want to subtract INTENSITY14.JPG from INTENSITY15.JPG. Ideally, the resultant image should look like SUBTRACT.JPG where the red dased box shows the part of the image which contains the liquid. But, I am getting the result as shown in S1.jpg which is undesirable. Below is my code. Any suggestions would be very much appreciated. Thank you.
a = imread('Intensity15.jpg');
b = imread('Intensity14.jpg');
dblSubtractedImage = double(a) - double(b);