Details:
Summary:
The magnitude of DeltaE between two simple fields, e.g., flat colors or logo colors, correlates well with visual assessment. As such, the use of DeltaE LAB to specify color tolerances of ink has been common in the graphic arts. However, there is no easy way to assess color difference quantitatively between two complex images, e.g., a pictorial color proof and its corresponding press sheet. Consequently, the practice of qualifying a color proofing system which conforms to a known printing condition or verifying printed products that match a contract proof remains visual and subjective. This paper uses a standard press characterization target (IT8.7/3 basic block) to quantify pictorial color image difference by colorimetry. Colorimetric measurement conditions and DeltaE(LAB) calculations adhere to the ANSI CGATS.5-1993 standard. Comparison of color images with the same colorant conditions and images with different colorant conditions were investigated. The quantitative analysis mainly focuses on the use of cumulative relative frequency (CRF) of the DeltaE distribution. We learned that a visual match between two color images can be specified by means of the CRF curve and its derived statistics. In addition, a visual match between two color images imposes a tighter colorimetric tolerance than process conformance as specified by solid ink density and dot gain.