Besides having cyan, magenta and yellow colorants, most of color printers include at least one extra colorant, black (K) in order to increase the density for shadow colors and to reduce colorants for printing shadow colors. There are numerous advantages of using GCR (Gray Component Replacement) technique: the chief advantages are (1) extension of color gamuts, especially of denser black, (2) improvement of image definition, and (3) substitution of relative inexpensive black ink to more costly colored inks.Unlike gamut compression studies, gamut extension is mapping from narrower original gamuts to wider reproduction gamuts. In this study gamut extension method was used in increasing color gamut, the major benefit of using black ink. In new method, black replacement is done in device-independent color space, and gamut is extended with increasing lightness reproducible range (CIE L* or J) and increasing chroma range, sequentially. In addition, observer experimental data of gamut extension studies was used for searching optimal black replacement.Two different evaluation experiments, quantitative and qualitative, were carried out. In quantitative experiment, color gamuts were compared between methods of existing GCR methods in commercial color printers and of this study. Furthermore lightness contrast values, i.e., reproducible lightness range, were compared. In qualitative evaluation (psychophysical), color imaging experts compared reproductions through two different methods. The results show new method outperforms existing black color replacement method.