DICOM image getting compressed while viewing in QOpenGLWidget

[pbinne]

Hi @all,
I need to get coordinates of dicom image using VTK and QT.
I tried PointPick example from VTK examples. It gives me x, y coordinates of QOpenGLWidget render window.
My dicom image displays at around center of render window. The dicom image is 576,576 originally, but in render window, it seems compressed less than 576,576 size.

Any better way to get seed values?
Please someone help me to get solution.
Thank you in advance.