![]() Cyan blue (an organic blue pigment with color index PB 15), for example, has a hue angle of about 240°. ![]() This implies that red has a hue angle of 0°. The hue angle range starts, by definition, at the positive side of the a *-axis and goes counter-clockwise. The hue of a color is quantified by its hue angle h ab (without * symbol) in the a *b *-plane, given in degrees (°). Hue and chroma can be visualized and quantified by using the a *b *-plane of the CIELAB color space. Colors of high chroma are said to be clear, bright or brilliant. Chroma is the amount of saturation of a color. Hue is the color tone or color name of a color. In the daily practice of those who work with paints, the representation of a color difference is often simplified as ΔE * or ΔE. Depending on the industry, the criterion for color approval can be strict, for example ΔE * ab < 0.3, or much milder, for example ΔE * ab < 1.5. The color coordinates of the batch and the reference are measured and the color difference Δ E * ab is calculated. But, how well must the color of the new batch match with the color of the reference? The answer to this question is a criterion in the quality control of a new batch of paint. The concept and quantification of color differences is important when a color must be matched or when a new batch of a paint must have a color that is close to the color of the standard paint, the reference. The color difference can be calculated by using the mathematical theorem of Pythagoras: A small ΔE * ab value implies that the colors are close to one another. Δ E * ab is the color difference of two colors, ‘1‘ and ‘2’, that have color coordinates L * 1, a * 1, b * 1 and L * 2, a * 2, b * 2, respectively. The color difference between two colors is the distance between the color points of the two colors. The new system is now universally used for the quantification of colors, even though often the simplified notation of the Lab-values, without the * symbol, is used. The asterisk ( *) symbol of L *, a * and b * indicates that this is the new color system it is the follow-up of the older CIELAB system. The a *-axis is the green-red axis and the b *-axis goes from blue (-b *) to yellow (+b *).Įach color is represented by a color point (L *, a *, b *) in the color space L *, a * and b * are the color coordinates of the color point. The so-called achromatic colors, the shades of grey, are on the L *-axis.Ĭhromatic (‘real’) colors are described by using the two axes in the horizontal plane. The L *-axis gives the lightness: a white object has an L * value of 100 and the L * value of a black object is 0. The 3-dimensional color space is built-up from three axes that are perpendicular to one another. The color of (coated) objects is visualized and quantified by using the CIELAB color space. The CIELAB Color Space The 3-dimensional CIELAB color space This article is about the fundamentals of this system. The good news is that there is a standard system that is used all over the globe: the CIELAB color system. Therefore, it is important to have an objective way to characterize colors of coatings, as well as to quantify differences between colors. ![]() Different persons have different perceptions of a specific color. Share this article: IntroductionĬolor is an important aesthetic aspect of coated objects. ![]()
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