How to normalize an image?

Hello digital image processing people,

I have a dataset of retinal images from the eye. I need to normalize them before processing to obtain accurate output. Here is my code:

The problem is after doing this, imshow display only black image. What must I do to fix this?

B is the image

gemiddeld=mean2(B)

standaard_afwyking=std2(B)

NormalizedArray = (B-gemiddeld) ./ standaard_afwyking;

GS = NormalizedArray ./ max(NormalizedArray(:))-min(NormalizedArray(:));

NormArrayU8 = uint8(255*(NormalizedArray+ 3)./6)

figure, imshow(GS);

[Narges M]

imshow(GS*255) usually fixes the problem. Let me know if it does.