The object returned is a standard Windows representation of an image, and may for instance be assigned to the picture property of a Visual Basic PictureBox.  It is also useful in many development environments for printing to standard (non-DICOM) printers.
e.g. in Visual Basic, an image may be printed simply by using
    Printer.PaintPicture Image.Picture, 100, 100
    Printer.NewPage
Like Copy, the Picture method returns a fully windowed version of the image “as seen”.

The image is always full size (1pixel:1 pixel), allowing full resolution.
PictureWithLUT likewise applies windowing to the image, but then applies an additional lookup table, as specified in the LookupTable parameter.  This final lookup enables the programmer to correct for non-linearities in the printer response, and is equivalent to the CalibrationCurve property of a DicomViewer (which corrects for screen non-linearities).  By use of an appropriate table, compliance with Part 14 of DICOM can be achieved.

For more details of how the final lookup table works, see CalibrationCurve.
 

DicomImage Object  | DicomImage Members