Черно-белое фото - luma
As applied to color signals, luma represents the brightness in an image (the "black and white" or achromatic portion of the image). Luma is typically paired with chroma. Luma represents the achromatic image without any color, while the chroma components represent the color information. Converting R''G''B'' (red-green-blue)sources into luma and chroma allows for chroma subsampling, enabling video systems to optimize their performance for the human visual system. Since human vision is more sensitive to luminance ("black and white") detail than color detail, we can optimize bandwidth for luminance over color.