Luma (video)

Luma in video technology represents the luminance or brightness component of a video signal. It is a grayscale representation of the image, carrying the intensity information without color data.

Luma, often denoted as Y, is a crucial element in color encoding systems like YCbCr and YPbPr. These systems separate the video signal into luma and chrominance (color) components, enabling various advantages:

• Backward Compatibility: Black and white televisions can display the luma signal from color broadcasts.

• Bandwidth Optimization: By encoding color information (chrominance) at a lower resolution or with less precision than luma, the overall bandwidth required for transmitting the video signal can be reduced. The human eye is generally more sensitive to changes in brightness than in color, justifying this approach.

• Compression Efficiency: Separating luma and chrominance allows for more efficient video compression algorithms.

Luma is calculated from the red, green, and blue (RGB) components of the video signal using a weighted sum. The specific weighting factors vary depending on the color space and video standard (e.g., Rec. 601, Rec. 709). These weights are chosen to reflect the relative sensitivity of the human eye to different colors. Green typically receives the highest weight, followed by red, and then blue.

The luma component is fundamental to many video processing operations, including brightness and contrast adjustments, sharpening, and noise reduction. These operations are often performed directly on the luma channel as they primarily affect the perceived brightness of the image.