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The text file method uses relative coordinates of fiducial marks as recorded with some device such as a microscope digitizer. Let us call these coordinates 'stage' coordinates. It also uses screen coordinates of fiducials in NIH Image. Before registration may take place, stage coordinates must be mapped to the NIH Image screen coordinate system. To do this, NIH Image reads the following, tab-delimited information from a text file. In every case, x-coordinates are followed by y-coordinates.

Line 1:	The screen coordinates of a point which is fixed for every image captured. In the sample fiducial file, this is the point which corresponds to the cross hairs on the microscope at capture time. This is the 'image center' point.
Line 2:	The location, in screen coordinates, of two fixed points in an image.
Line 3:	The location, in stage coordinates, of these same two fixed points.
Line 4:	(and each subsequent line) the locations, in stage coordinates, of the 'image center' and at least two, but no more than 12, fiducial points for an image to be registered.

Obviously, the stage coordinate system may not change in rotation, translation, or scale in the middle of a set of images being captured, so it is advisable to record stage coordinates at the time of image capture (without changing camera settings or the position of the object whose image is being captured).