The role of black printing in color separation

In theory, CMY can reproduce thousands of colors, including black of course. But this is in terms of the ideal ink, and the actual ink we use is still a certain gap from the ideal ink. Specifically, images printed in three colors of C, M, and Y are not “spiritual”, and the density of dark places cannot be maintained, and the image contrast is not sufficient. Even the density of black generated by Y100%+C100%+M100% is still Not enough, black is not very dark.

And in the photo printing, the image density of yellow, magenta, and blue is superimposed and printed out. The density of the picture is not enough, the outline of the picture is not clear, the contrast of the picture is insufficient, and it is not enough spirit. In order to make the image appear more spiritual, people add a black version when printing to express the outline of the image. Therefore, the black version is designed to compensate for the lack of density in the high-density (dark) areas of the yellow, blue and green primary inks. At the same time it can also improve and enhance the image frame outline.

Therefore, the black version of the contour and skeleton that was created for copying the dark areas of the original document is called a short tone black version or a contour black version.