(3,n)-門檻式視覺機密分享是(k,n)-門檻式視覺機密分享的一種特例，不過在典型的(3,n)-門檻式視覺機密分享的研究會產生設計複雜、還原影像黑白色差不佳、機密影像只適用於黑白影像、像素擴展等問題。為了解決上述幾個研究限制，本研究提出一個應用組合數學公式求解的非擴展型(3,n)-門檻式視覺機密分享。相較於其他相關研究，本研究具備下列幾項優點：(1)設計概念十分單純，易於實作。(2)還原影像的黑白色差值優於或等於其他(3,n)-門檻值機密分享的研究成果。(3)本研究所提出的分享模型適合任何型態的機密影像。(4)分享投影片的大小將與機密影像相同。

(3,n)-threshold visual secret sharing ((3,n)-VSS) is a special case of (k, n)- threshold visual secret sharing. In previous related (3,n)-VSS researches, it has following drawbacks: complex design method, poor black-white contrast of the restored image, only suitable to binary image, and expanded pixels. In order to solve the above problems, our study proposed a novel approach to design (3,n)-VSS using combinatorics. Compared to other related studies, this study has the following advantages: (1) design concept is simple and easy to implement; (2) the black-white contrast of the restored image is better than other (3,n)-VSS researches; (3) the secret type is more suitable to grayscale and color image; (4) the transparencies (shares) are the same size as the secret image.