find noise from histogram

sir the images in the link below are the histograms i got... i want to find whether any kind of noise exist...

As per the link in

http://www.mathworks.in/matlabcentral/answers/131873-how-to-know-whether-noise-in-a-image

it tells that "If there is no noise it should be a big spike at zero"

please can anyone tell me why there are 2 spikes, one spike at zero and one spike at 1, as shown in the link below.... what does that mean?... please do reply....

http://oi57.tinypic.com/2dklv5t.jpg

Answer 1

[Image Analyst]

Did you cast the images to double before you subtracted them? You need to. If you did that and you get spikes at 0 and 1 then that means there are a bunch of pixels that are the same in the two images and there are a bunch that differ by only 1 gray level.