The Extract Lab component extracts an L, a or b channel from the source image or color according to the CIE L*a*b color model. L stands for lightness, and a and b are chromaticity coordinates. The channels are extracted as grayscale images, where light areas correspond to higher channel values, and dark areas correspond to lower channel values. For more information on the CIELab color model, see this Wikipedia article on the L*a*b color model. Extract Lab is a map component, it can be located in the Channels category on the Components Bar.
Source: Map Input
Provides the source image or color from which the specified channel will be extracted.
Specifies a channel to extract: L, a, or b. When a map component is connected to this input, the number of the selected list item is determined separately for different image areas by the HDR brightness level of the image supplied by that component. The item number is calculated as the brightness level rounded to the nearest integer: the brightness level of 0 to 0.5 corresponds to the first item, the level of 0.5 to 1.5 to the second item, and 1.5 to 2.5 to the third item. Out-of-range values are clipped, which corresponds to the last item of the list.
Invert: Map Input
Inverts the extracted channel. When a map component is connected to this input, the state of the checkbox is determined separately for different image areas by the brightness level of the image supplied by that component. The brightness level of 0 to 50 corresponds to unchecked Invert, and the level of 50 to 100 corresponds to checked Invert.
