How to Create a Bitmap with a Given Resolution:
Verify that the option File > Free Size is checked.
Choose iNMR > Preferences and click Output. The pair of parameters that set the resolution of the picture are at the bottom of this panel: Resolution and Line Thickness when copying and exporting. The most important one is the Resolution. If you need a resolution x times higher than that offered by the screen, set resolution = x.
Also set the line-width to a small value. When the value is 1, the plot looks good on the screen, but may look too coarse when printed. A value of 0.25 gives a faint line, almost invisible on the screen. 0.5 is a good compromise. You are encouraged to experiment by yourself.
Choose File > Export. iNMR opens the standard dialog to save a file. Choose a name and a destination for the picture. Also choose one of the following file formats: TIFF, Windows Bitmap, PICT, JPEG and PNG (this is our preferential order). If you are going to send the picture to a typographer, he can tell you which format is better. Don't choose PDF, because it generates a vectorial representation, not a bitmap.
The resulting picture will actually be x times wider and higher than the window and the resolution will be 72 dpi. The line-width will also be x times thicker. It will be enough, however, to scale the picture down x times (any program is capable of doing such scaling) and it will become exactly what was needed in the beginning.