8 bits dicom with rescale slope intercept images with voilut could lead to odd rendering

8bits Dicom images with voilut rescale slope intercept could lead to odd rendering.
Normal display
![image](https://user-images.githubusercontent.com/1135156/45154486-07665780-b1d8-11e8-8ca2-e496cd20e2d3.png)
Actual display
![image](https://user-images.githubusercontent.com/1135156/45154450-fae1ff00-b1d7-11e8-9251-566e09c217ad.png)
