Y weights reflectance by the eye's sensitivity, which peaks in the green near 555 nm, so it sums up perceived lightness in one value. ISO opacity is calculated from Y readings rather than from a single wavelength, and Y is also an input to CIE whiteness. It converts directly to CIELAB L*.
Opacity is calculated on Y, not 457, so the yellow dye trial won't hurt opacity the way it hurts brightness.
Also heard as
- Y
- Y value
- tristimulus Y
Related terms
Printing opacity
Opacity calculated as single-sheet reflectance over black divided by the reflectance of an opaque pad of the same paper.
CIE whiteness
Formula-based whiteness index computed from luminance factor Y and chromaticity, under D65 or C illumination.
Standard observer
CIE model of average human color vision, defined for a 2-degree or a 10-degree field of view.
CIELAB
Color space describing a color by lightness L* plus a* for red-green and b* for yellow-blue.