For dichromats to receive the information represented incolor images, it is important to study contrast improvement methods andquantitative evaluation indices of color conversion results. There is an indexto evaluate the degree of contrast improvement and in this index, the contrastfor dichromacy caused by the lightness component is given importance. Inaddition, random sampling was introduced in the computation of this index.Although the validity of the index has been shown through comparison witha subjective evaluation, it is considered that the following two points shouldbe examined. First, should contrast for normal trichromacy caused by thelightness component also be attached importance. Second, the influenceof random sampling should be examined in detail. In this paper, a newindex is proposed and the above-mentioned points are examined. For thefirst point, the following is revealed through experiment. Considerationof the contrast for normal trichromacy caused by a lightness componentthat is the same as that for dichromacy may or may not result in a goodoutcome. The evaluation performance of the proposed index is equivalentto that of the previous index overall. It can be said that the proposed indexis superior to the previous one in terms of the unity of evaluating contrast.For the second point, the computation time and the evaluation of significantdigits are shown. In this paper, a sampling number such that the numberof significant digits can be considered as three is used. In this case, thevariation caused by random sampling is negligible compared with the rangeof the proposed index, whereas the computation time is about one-sevenththat when the sampling is not adopted.
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