What is benefit when convert signed 16 bit to unsigned 8 bit in medical image? I have an image with its type is 16 bit signed. I see some paper, the author often convert it to unsigned 8 bit. But they did not explain why they do it. Could you explain what is benefit of this work? And How to implement it by matlab code?
Many image display devices only have an 8-bit DAC.  So if one wants to analyze only what will be displayed on such a device (without added dithering or noise filtering, etc.), one can convert to that 8-bit format and potentially save storage memory.  Many standard image file formats also only support 8 bits of luminance, so the same is true for data planned to be stored or transmitted in such a format.  

However, this process is lossy, and will remove information that a display supporting greater luminance resolution (10-bit DAC, etc.) can display.