Luminanskomponenten

Luminanskomponenten, commonly called the luminance component, is the part of a color signal that encodes brightness information independent of chromaticity. In most color models used in imaging and video, the luminance component is designated by Y and serves as the reference axis for perceived lightness.

Relation to color spaces: In digital video, Y is paired with chroma components such as Cb and Cr (or U and V) in YCbCr or YUV color spaces. The Y component is intended to approximate the human eye’s sensitivity to brightness, enabling efficient compression and flexible processing such as grayscale rendering by discarding chroma.

Computation: The luminance component is typically computed as a weighted sum of the red, green, and blue channels. Common coefficients depend on the color space: for Rec. 601 (standard-definition), Y ≈ 0.299 R′ + 0.587 G′ + 0.114 B′; for Rec. 709 (high-definition), Y ≈ 0.2126 R′ + 0.7152 G′ + 0.0722 B′. Here R′, G′, B′ are gamma-corrected (non-linear) RGB values. In linear RGB, luminance is often defined as Y_linear = 0.2126 R_linear + 0.7152 G_linear + 0.0722 B_linear, which maps to the Y axis of the CIE XYZ space.

Note on Y′ vs Y: Y′ (luma) is the non-linear, gamma-corrected version used in consumer video, while Y is the linear luminance value used in color science and display pipelines; Y′ is designed to match perceptual brightness after gamma encoding.

Applications: Luminance is essential for grayscale imaging, edge detection, video compression, chroma subsampling, and display-intensity mapping.