finger vein image enhancement by Gaussian high-pass filter

Dear Gen. I need your kind support in my issue, in my project i have to use a symmetrical modified Gaussian high-pass filter for image enhancement as in below snap shoot,

the image in top is the gray input image and the image down is the filtered image by Gaussian high-pass filter the purpose of using the filter is to enhance the vein of finger image.

the symmetrical modified Gaussian high-pass filter used for enhancement used the below formula:

H(x,y)=a*(1-e^(-(distance^2)/(2*d^2)))+b
where : distance=sqrt((x-p)^2+(y-q)^2) , a=12.5 , b=-4 and d=12.

but when i coding the above formula and test it with a gray input finger vein image, there is no any change between the input and output image. my code as below:

[m, n]=size(grayimage);
f_transform=fft2(croppedImage);
f_shift=fftshift(f_transform);
p=m/2;
q=n/2;
d0=12;
for i=1:m
for j=1:n
distance=sqrt((i-p)^2+(j-q)^2);
x(i,j)=12.5*(1-exp(-(distance^2)/(2*(d0^2))))-4 ;
end
end
filter_apply=f_shift.*x;
image_orignal=ifftshift(filter_apply);
image_filter_apply=abs(ifft2(image_orignal));
figure(5)
imshow(image_filter_apply,[])

the input gray finger vein image is in attach any kind support for my issue? kind regards