New Test Methods for Evaluating the Humidity-Fastness of Inkjet Prints

The humidity-induced loss of line and edge quality in inkjet prints is due to lateral migration of the colorants within the image layer, whereas color and tone scale changes can be caused by both lateral and vertical diffusion of the colorants. The migration effects vary with colorant mixtures and ink loading. In an earlier study, we showed that ∆E measurements for solid-fill areas of color did not correlate with line quality degradation. However, ∆E measurements made with a 4mm aperture instrument of color patches printed in a simple 72 dpi “checkerboard” pattern (see Figure 1) correlated well with line quality degradation as judged by a psychophysical scaling experiment.1 In this paper, a “line quality retention” (LQR) rating has been derived from the results of the original study. The I* metric was recently developed to colorimetrically evaluate changes in image appearance over the full tonal and color gamut range of modern digital printing systems using a comprehensive approach not previously undertaken with more conventional densitometric test methods.2 The I* method has also been programmed in a software application with enhanced features that allow one to evaluate not only the overall I* results but also filter the data for image specific color and tonal ranges (e.g., near grays, skin tones, highlights, shadows, etc). The application can also show data distributions within a large sample population of color patches.