# Two points

Between two points we can draw a straight line segment. The division of this segment into a number of equal segments produces a gradient color between the two points (figure 2).

We have seen that the CIELAB  system has three axes of which two correspond to blue-yellow and red-green antagonisms. This way of locating colors is not the most useful. Generally speaking, we prefer to find a hue with a color wheel. The CIE so proposes a polar coordinate system for CIELAB space called CIELCH in which L corresponds to the L of CIELAB, C gives the distance of the color to the achromatic vertical axis of black to white and H the angle of hue expressed in degree. Zero degree corresponds to the red color.

If we use LCH coordinates in a Cartesian system we could transform the circle of hues into one of the axes. Consider then a plane defined by two axes, for example, for the abscissa and the ordinate, H and L or H and C with respectively C or L constant. Two points in this type of plan define a segment that can go through several hues. It is the equivalent of a circle in Cartesian coordinates.

Figure 3 shows a HL plan view with C = 50 and the segment defines by coordinate points [66, 50, 263] and [66, 50, 49]. This segment is divided into ten parts, we therefore have ten intermediate colors.

Figure 4 shows a graphical usage example of this gradient.