A Color Graln Ruler for the Measurement of Print Graininess

In a photographic system, the random variations in otherwise uniform responses to exposing light are referred to as grain. This two-dimensional random noise is characterized objectively by the RMS granularity. The subjective impression of this noise is termed graininess. Bartleson demonstrated that a logarithmic relationship exists between the RMS print granularity and perceived graininess as measured on an interval scale. Subsequently, Maier and Miller described the first grain ruler, a technique whereby graininess can be measured or visualized quickly and directly. Although observers were able to successfully use this technique to directly measure graininess, large interobserver variability was found in actual use. In this paper we explain the source of this variability and present an improved grain ruler for use with color reflection materials. The KODAK Color Grain Ruler, created via digital image simulation techniques, allows the direct measurement of the graininess of color reflection prints with a minimum of interobserver variability. The KODAK Color Grain Ruler has applications for both conventional photographic prints and, within certain limitations, the assessment of two-dimensional random noise in digitally generated reflection prints.