Color temperature same as chromaticity? That is a question that lingers in the mind of people who are new to the concepts of videography. It goes beyond the particular colors being captured by video cameras. It involves international standards and the capability of video cameras in capturing the different elements of an image. Here are a few facts on both concepts and some information about their relationship. The first thing you need to know is that color temperature is different from chromaticity. While the two concepts may not be one and the same, they have a very intimate relationship.
This concept refers to the purity of a color. The presence of black, white and gray in a particular color determines its chromaticity. High chromaticity means the color is pure and it has a more vivid look. Low chromaticity means the colors have no hue and appear to be shades of black, white and gray. This property of color is used in color matching, which has several real life applications in photography, publishing and videography.
The theory is that we can describe one color using three numbers. These numbers correspond to three chromaticity values that are achieved via determining the intensity of the light source of different colors. Mixing these three light sources will produce the matching light to a fixed spot of light which is commonly known as the test light. The process of matching the two spots of light, which is the test light and the matching light, is called color matching. This procedure is used to create a chromaticity diagram which can then determine the range of colors that can be produced by the light emitted by a display device like a computer monitor or an LCD display on a video camera.
This color matching theory dictates that observers of the two spots of light can match them using several light sources with different intensities. The assumption is that only three light sources are required to successfully achieve this. The values for each of the light sources are used to get the chromaticity coordinates which are then used to plot the chromaticity diagram. We can assign these light source values to X, Y and Z variables. The Y variable is defined to have an equal luminance with the test light. The chromaticity coordinates are then acquired using the following formulas:
x = X / (X+Y+Z)
y = Y / (X+Y+Z)
z = Z / (X+Y+Z) = 1 – (x+y)
The coordinates, usually just x and y, plus the Y value are used to plot the chromaticity diagram of a test light. These diagrams produce triangles that show the gamuts of devices like computer monitors and LCD displays. This means that all colors and hues within the triangles represent the range of colors that devices are capable of displaying. This same color matching theory and diagram concept is behind the definition of color temperature.
A light source has a color temperature and this element is determined by color matching the color of the light source with the emitted color of a black-body radiator at said temperature. This simply means that, in order to match the color of the light source, the temperature imposed on the black-body radiator, which is an ideal component, should be adjusted. The temperature that produces the matching color is deemed the color temperature and it is represented in units of absolute temperature which is Kelvin (K). In relation to chromaticity, the color temperature of a color is just another way to describe color by using different variables.
In essence, chromaticity is just one way to describe colors. Its different levels can be used to categorize colors. Adjusting it can make the color of video clips look more vivid or simply black and white. Simply put, chromaticity ranges from colors being dull and dead to colors being brilliant and vivid. Color temperature on the other hand ranges from red and yellow tones to blue and white tones. Red and yellow represent warm lighting while blue and white represent cool lighting. These extremes and everything in between can help you set the mood of a particular video clip.
So, is color temperature the same as chromaticity? Not quite. They are two different elements and concepts that you can use in modifying how your videos look and feel. Knowing more about them can help you set up your video equipment in such a way that you can achieve the right mood and color quality you are aiming for.
Photo Courtesy of Wikimedia Commons / Supplied by PAR