But if the luma component Y' itself is instead used directly as a grayscale representation of the color image, luminance is not preserved: two colors can have the same luma but different CIE linear luminance (and thus different nonlinear as defined above) and therefore appear darker or lighter to a typical human than the original color. Similarly, two colors having the same luminance (and thus the same ) will in general have different luma by either of the luma definitions above.