X is the gray level in Walter's answer. Did you try to do it, like this:???
X = 0:255;
P = 3;
quantizedGrayLevel = X - mod(X,2^P)
fprintf('Original Gray Level, New Quantized Gray Level\n');
for gl = 1:length(X)
fprintf('%10d becomes %10d\n', X(gl), quantizedGrayLevel(gl));
end
