Gamut Mapping Algorithm Using Lightness Mapping and Multiple Anchor Points for Linear Tone and Maximum Chroma Reproduction

of the reproduction’s. Therefore, if the lightness values of the maximum chroma in the two gamuts are not located at the center of the lightness axis of the two media, the parametric GMA will produce a different color change in the bright and dark regions. In this condition, if linear compression or soft-clipping compression is applied to the lightness mapping, the lightness value difference between the two gamuts is increased. As the lightness value difference is increased, so the difference in the color change is also increased and it becomes difficult to maintain the maximum chroma in the gamut mapping process.11 Thereafter, if a parametric GMA using an anchor point (a center of gravity on the lightness axis) is applied to the original image, the lightness of the bright regions will decrease while the lightness of the dark regions will increase to include the original colors in the reproduction gamut. As a result, the lightness range is also reduced along with the contrast. Furthermore, if the anchor point is not located at the center of the lightness axis of the two media, the parametric GMA utilizing the anchor point will produce a different color change in the bright and dark regions. As the lightness value difference of the maximum chroma of the two media increases, so the difference in the color change will also increase. In addition, the input colors mapped towards an anchor point in the same region will also exhibit a different color change, because the conventional GMA maps the input colors along lines with different slopes. As a result, these algorithms produce sudden color changes on the boundaries between mapping regions. Accordingly, to solve these problems, a lightness mapping is proposed that minimizes the lightness difference of the maximum chroma between two gamuts and produces the linear tone in bright and dark regions. In this process, a lightness mapping is used that is based on both the shape of the original and the reproduction gamuts at a particular hue angle. Initially, the reproduction gamut Introduction