Applying non-linear compression to the three-dimensional gamut mapping

Gamut mapping is a technique to transform out-of-gamut colors to the inside of the output device's gamut. It is essential to develop effective mapping algorithms to realize WYSIWYG (What You See Is What You Get) color reprodu ction.(1) We had previously found that three-dimensional gamut mapping Is s uperior to the two-dimensional mapping, when we applied Mahalanobis distanc e as a color difference equation, such as BFD color difference formula.(2,3 ) However, in our previous experiments, a clipping method was used that map s all out-of-gamut colors to the surface of the gamut, and no change was ma de to colors inside the gamut. Since this method could possibly cause loss of gradation in an image, we had investigated non-linear compression for th e three-dimensional gamut mapping in this study. The results of visual expe riments indicated that preferred compression method depends on image conten ts. If the saturated colors that are out-of-gamut contain high frequency co mponents, a certain degree of compression was needed. On the other hand, if those colors only have gradual change with low frequency components, clipp ing method was preferred.