Research on large color difference evaluation using printed samples
A grey-scale psychophysical experiment was carried out for evaluating color differences using printed color patches. In total, 100 pairs of printed samples were prepared with an average ΔE*ab of 13.8 units. Each pair was assessed 60 times by a panel of 20 normal color vision observers. The visual results were used to test the existing color-difference formulae. The results showed that all formulae gave quite satisfactory performance except OSA-Ep-Gu, which is the formula for calculating the magnitude of small-medium color difference. The optimized kL values were used to compare with the medium color difference (MCD) of the earlier studies. The results showed that they agreed well with each other.
APPLICABILITY OF STANDARD GREY SCALE FOR REPORTING PERCEIVED COLOR DIFFERENCE OF PRINTS ENHANCED WITH PEARLESCENT PIGMENTS
Printed materials that exhibit goniochromism pose a challenge not only for colour measurement but also for estimating colour differences. A common procedure for determining perceived colour difference implies assessing colour pairs by means of a standard grey scale. This method was proven to be adequate for estimating, among others, perceived differences of low chroma goniochromatic samples found in the automotive industry, as well as for assessing colour differences of conventional prints. In this work, we were interested in the applicability of the same approach for estimating colour differences of printed samples enhanced with pearlescent pigments. Such prints are regarded as goniochromatic and depending on the type of the pigment, can exhibit very high chroma in angles close to specular reflection. This may pose a problem in evaluating colour differences because grey scale only shows a change in lightness. In addition, in some illumination/viewing geometries the differences between the two samples can be higher than those presented in the grey scale. Nine colour pairs (low-chroma digitally printed samples enhanced with three types of pearlescent pigments) were assessed in six viewing/illumination angles by a panel of ten observers. Our results show that chroma of the samples did not influence significantly interand intra-observer agreement, implying that grey scale references can be used for determining the perceived differences between chromatic samples. SDC grey scale provided sufficient range of colour differences only for the limited set of printed samples, leading to the conclusion that for assessing the differences of printed samples enhanced with pearlescent pigments it is necessary to use reference scale with higher difference range.
Geologic proof on paleo-glaciation remains in Laoshan Mountain
Laoshan Mountain is the highest mountain in China coast.Various typical geomorphic features of glarosion,glacial deposition,rare glacial moraine coast and glacial moraine fans in east are well developed in Laoshan Mountain.Well preserved four glacial epochs are identified in Laoshan Mountain.In early Pleistocene,the altitude of snowline ranged from 60 m to 90 m in east.More than sixty paleo-glacial tongues were developed in Laoshan Mountain,some of them which located in east extended into the Yellow Sea.Sporopollen analysis indicates that the climate in Laoshan Mountain is very cold during the ice age.Multi-modal grain-size probability curves of the moraines are the typical characteristics of sediments deposited by glaciation.Regional landforms and climatic conditions are the key factors dominating the altitude of snowline during the ice age.