zero-mean deviation on image

I can find to obtain the right output, after doing the statistical normalization on retinal image. It is to standardize all images, because some are dark and other are too light.

Here follows my code:

DefaultName = 'C:\Users\nvg\Desktop\Hoofstuk 3\Matlab\images';

[FileName,PathName,FilterIndex] = uigetfile(FilterSpec,'Image file selector',DefaultName);

if (FilterIndex >0)

    LeerNaam = strcat(PathName,FileName);                       % get filename

    OriginalRGB = imread(LeerNaam);                             % read image
end
figure, imshow(OriginalRGB);

gemiddeld=mean2(OriginalRGB)

standaard_afwyking=std2(OriginalRGB)

NormalizedArray = (OriginalRGB-gemiddeld) ./ standaard_afwyking;

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

I want it to be in linear format between 0-255?

[Valeska Pearson]

I am getting either a black image or a white image. Why can't I get a normalized version image?