Photometric Measurement of Dot Area.

The principles of measurement of halftone dot areas with a photometric instrument such as a densitometer are reviewed briefly and some discussion of the calibration of such instruments and their standardization is presented. A precise method of measuring ordinary halftone dots by employing semi-dark field illumination is presented. The fringe, which ordinarily surrounds all first generation halftones and which ordinarily interferes with an accurate measurement of dot area, can be effectively eliminated by proper illumination. The details of this technique and some examples of its accuracy are given. The significant fact of this development is that an accurate measure of dot area is obtained, even though the amount of fringe is a variable with a single film-developer combination.