Chrominance is the hue of a colour. This can be used together with the luminance (the brightness) and the saturation (the purity of the colour) as an alternative to specifying the red, green and blue (RGB) components. This is useful because the eye perceives variations of chrominance and saturation across an image much less sharply than variations of luminance. Hence these latter can be presented at lower definition with no visible degradation in the image, so saving storeage or transmission bandwidth. It also allows a graphic designer to select a range of related colours by varying just one of those three parameters.