PVC-3 White Noise Stimulus Data

Hello,

I'm having trouble understanding the stimulus data for the white noise case. I thought it was Gaussian white noise but it does not seem to follow a Gaussian distribution. I loaded the data with the following code and then plotted all of the pixel values and attached the histogram.  It seems as if the data is somehow binned into 15 bins instead of spanning all 256 values. Is this stimulus Gaussian white noise and if so, why does the histogram look like this? Thanks for your help!

filenameM = '/stimulus_data/wn2-64p-50h-2m-mn125-ct045.m';

fidM = fopen(filenameM);

c = fread(fidM, 'uint8');

hist(c,250);