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L star in CIELAB is defined so that

  • A.it runs from minus one hundred to plus one hundred
  • B.a value of fifty corresponds to a mid grey in appearance
  • C.a value of fifty corresponds to fifty per cent reflectance
  • D.it is directly proportional to the luminance factor

Answer: B

Correct answer: a value of fifty corresponds to a mid grey in appearance

\( L^* \) is a perceptual scale, so its midpoint is the grey that looks halfway between black and white - which reflects about 18 to 20 per cent, not 50. That gap between appearance and physics is the whole reason for the cube root transformation.

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