1. A method of automatically controlling digital printing of a document print job on media sheets comprising: (a) providing a print engine; (b) disposing a first sensor for measuring an image on a printed sheet; (c) disposing a second sensor for measuring an image on a surface internal to the print engine; (d) measuring an image on a printed sheet with the first sensor; (e) measuring an image on a surface internal to the print engine with the second sensor; (f) determining a performance metric of the image on the printed sheet and, if acceptable, saving the measurement of the image on the surface internal to the print engine from the second sensor as a reference, and if not acceptable, calculating and applying a control signal and repeating steps (d)-(f); (g) executing the print job and periodically measuring an image on the surface internal to the print engine using the second sensor and comparing with the saved reference; and, (h) repeating steps (d)-(f) if the comparison in step (g) is not within an acceptable range; and, continuing the print job if the comparison of step (g) is within an acceptable range.