thank you for your reply.
I did it in the below way:
mean = np.mean(data)
max = np.amax(data)
min = np.amin(data)
new_data = np.empty((256,256,94))
for i in range (256):
for j in range (256):
for k in range (94):
new_data[i,j,k] = (data[i,j,k]-mean)/(max-min)
where data is my input that has the shape of (256,256,94), its a tiff file.