'**SUMMARY**
Sets an ROI for the scanner in the current resolution.  The
two parameters, topleft and bottomright, will default to the
device extents, so the ROI can be reset by calling setROI with
no parameters.
The ROI is set by SANE in resolution independent units (default
MM) so resolution can be changed after ROI has been set.
**RETURNS**
None
**EXAMPLES**
>>> scan = Scanner()
>>> scan.setROI((50, 50), (100,100))
>>> scan.getImage().show() # a very small crop on the scanner'

def setROI(self, topleft=(0, 0), bottomright=((-1), (-1))):

    self.device.tl_x = self.px2mm(topleft[0])
    self.device.tl_y = self.px2mm(topleft[1])
    if (bottomright[0] == (-1)):
        self.device.br_x = self.max_x
    else:
        self.device.br_x = self.px2mm(bottomright[0])
    if (bottomright[1] == (-1)):
        self.device.br_y = self.max_y
    else:
        self.device.br_y = self.px2mm(bottomright[1])
