Apply Gaussian Function for a image before performing Fourier Transformation in OpenCV.

Question

I am trying to implement the algorithm specified in following paper(Sec 3: Ridge candidate extraction part).

http://ai.pku.edu.cn/aiwebsite/research.files/collected%20papers%20-%20palmprint/Feature%20extraction%20method%20for%20palmprint%20considering%20elimination%20of%20creases.pdf

But while proceeding there are lot of negative and very smaller numbers were generated while applying gaussian filter. Is there a predefined functions in OpenCV to use for this kind of operation?