Details:
Summary:
Spot color printing has a significant role in maintaining consistency in shade reproduction on different substrates. For consistency in quality reproduction, the first step is color measurement, but because color is a psychophysical quantity, numerical shade approval is not sufficient. Thus, a shade must be approved visually as well as numerically. Visual-instrumental agreement is very important in color approval. A shade may be reproduced in different sample sizes, and then due to sample size, a viewing field angle must be selected. Viewing field changes may change visual perception of the same shade. Generally, shades that are closer to the boundary of quadrants are more likely to be subject to perceived color changes. This study is carried out for colors that fall near quadrant boundaries in CIEL*a*b* color space. In this work, colors that have a* or b* absolute values less than 2 and change their quadrant after switching field of viewing are considered. Psychophysical experiments were conducted considering 2 deg human observers, and the results show that visual-instrumental agreements are worse at quadrant boundaries. It was � found that in the case that the shade falls closer to boundary of quadrant, setting tolerance limits becomes very difficult. If the same color is plotted in different color spaces such as LABNHU, LLAB, RLAB or ZLAB and comparison is carried out, the RLAB model seems to be more useful in the spot color approval process.