Characterization of Plate Images, Part 2 - Integrating Sphere Densitometry

This paper and it's predecessor Characterization of Plate Image, Fact or Fantasy, (Cavin, 1996), now called Part 1 - 0/45i Densitometers, report on the use of photometric devices to characterize metal plate halftone images. Part 1 - 0/45i Densitometers reported on results of different 0/45i densitometers to measure dot area of metal plates. The design included a variety of plates and grain surfaces. Results were poor. Part 2 - Integrating Sphere Densitometers reports on results of different integrating sphere spectrophotometers to measure dot area of metal plates. Specular components included and excluded was examined. A 0/45i densitometer was also included in the design. Various plates with differing grain surfaces were measured. The conclusions of Part 1 concerning 0/45i densitometer are confirmed in Part 2. In addition, the variability of density as stated by densitometer manufacturers was used to determine the range of dot area that could be expected when measuring tint patches. The use of statistics has disclosed the following conclusions based on seven null hypotheses that are discussed in depth in the experimental section of the paper: 1. - Based on manufacturers' published tolerances for density of 0/45i densitometers, percent dot area cannot definitively be measured. 2..-.Based on measurements of images on grained metal plates using 0/45i densitometers, percent dot area cannot definitively be measured. 3..-.Based on measurements of images on grained metal plates using integrating sphere spectrophotometers, percent dot area calculations from derived spectral densities is too variable to measure metal plates. 4..-.Spectrophotometry is less variable than 0/45i densitometry. 5..-.Depending on the spectrophotometer manufacturer, specular excluded integrating sphere measurements are preferred. 6..-.Small dot values below 10% are difficult to read using either RD45 or integrating sphere devices. 7..-.Tint measurement from smooth grained plates are more variable than medium to rough plates.