Chroma vs Saturation
In recent weeks, the blog has finished with a little observation about color theory. In light of the Christmas holidays being celebrated by many people around the world, this week and next week the blog will both begin and end with a short observation about color theory.
Chroma
Since this is the end of my observations on the properties of color, let’s do a little re-cap. There are three properties: hue, value (brightness) and saturation.
Hue is a fairly easy concept. It is the dominant color in a color. While the concept is easy, figuring out the hue for a particular color may or may not be easy. For example, I had to Google what the hue of a brown is. The answer is, for most browns, the hue is orange. We call hue a quantitative property of a color. Whatever the hue is for a particular color, it never changes.
Value, or the lightness and darkness of a color, is also a fairly straightforward concept. If you add white to the color it gets lighter and we call it a tint. If you add black to a color is gets darker and we call it a shade. Like hue, value is also a quantitative property of a color. It never changes. Now that seems pretty counterintuitive. We all know that if you take a photo in bright light the colors will look very different than if the same picture was taken when it is dark. The reason that value is unchanging is because of the way that it is scientifically defined. A value is determined by how light or dark it is relative to a similarly lit white area. As the light brightens or darkens the white area, it brightens or darkens the color areas that are similarly illuminated by exactly the same amount.
Saturation is the relative purity of a color. If black, white or grey is added to a color, it is a less pure color. It is a qualitative property of color because our perception of the purity varies with light and other environmental aspects, like how far the color is away from us.
Sometimes, actually often, the term chroma is used interchangeably with saturation. Honestly, the distinction for most photographers is not especially material. However, if you read much about color theory, the lack of preciseness in the use of these two terms can be very confusing.
Chroma is defined on the website, Munsell Chroma, as the “colourfulness of an area judged as a proportion of the brightness of a similarly illuminated area that appears white or highly transmitting.” Chroma and saturation both measure how pure a color is. Saturation is a qualitative measure about how pure the color looks based on how it appears in its environment and the light. Chroma is the quantitative measure of how pure a color is compared to a similarly illuminated white area. Like value, the chroma is an attribute of the color because it does not vary when compared to a similarly illuminated white area, even if the illumination or environmental factors vary.