You need to use a Canvas object.
With
Canvas1.DrawBitmap(Bitmap1 As Bitmap, SrcRect As Rect, DestRect As Rect)
you can copy a part of the Bitmap1 bitmap (SrcRect) source rectangle to the Activity (DestRect) destination rectangle or an ImageView.
If the Widths and or Heights of both rectangles are different, the bitmap is rescaled according to the rectangles sides ratios.
Best regards.