The a star and b star axes in CIELAB are unbounded, which means
Answer: C
Real colourants reach values well over one hundred in some hues. The practical limits are set by available materials rather than by the space. The mathematics imposes no ceiling at all. Real colourants set the practical limits.
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The CIELAB colour solid for real surface colours is irregular because
Answer: D
Correct answer: attainable chroma varies greatly with hue and lightness
No colourant can produce a highly saturated dark blue or a highly saturated light yellow, so the solid of real colours bulges where the pigments are strong and pinches where they are not. Yellows reach their maximum chroma at a high lightness and blues at a low one, which is what makes the solid so lopsided.
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Assertion (A): The CIELAB space is unbounded while the solid of real colours is not.
Reason (R): Attainable chroma is limited by the colourants available rather than by the mathematics.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Nothing in the equations limits how large \( a^* \) and \( b^* \) may be, so the space extends indefinitely. What limits real colours is that no surface can reflect more than the light falling on it, and no available colourant is more selective than it is - a physical bound rather than a mathematical one.
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A chromatic adaptation transform such as CAT02 is used to
Answer: B
It maps a colour under one illuminant to its appearance match under another. The von Kries form scales the cone responses independently. It maps a colour across two adaptation states. Cone responses are scaled independently.
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Consider the following statements about chromatic adaptation transforms.
1. They predict corresponding colours across illuminants.
2. They operate by scaling responses in a cone-like space.
3. They convert reflectance data into tristimulus values.
Answer: C
Correct answer: 1 and 2 only
Statements 1 and 2 describe what a chromatic adaptation transform does: predicting the stimulus that would look the same under another illuminant, by scaling responses in a cone-like space in the manner of von Kries. Statement 3 describes the ordinary tristimulus calculation, which is a different operation performed at a different stage.
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Assertion (A): CAT02 operates in a sharpened cone response space rather than in XYZ.
Reason (R): Scaling in a more nearly cone-like space predicts adaptation more accurately.
Answer: D
Both are true and the reason gives the improvement over CIELAB. The sharpening is an empirical adjustment fitted to experimental data. XYZ is not close enough to a cone space. Sharpening improves the prediction measurably.
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Corresponding colours are pairs that
Answer: A
Experimental sets of such pairs are used to fit and test adaptation transforms. They are the empirical basis on which every such transform rests. Corresponding colour data constrains the fitting. Experimental pairs are the empirical basis.
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The CIE has recommended CIEDE2000 rather than Delta E ab because CIEDE2000
Answer: B
Lightness, chroma and hue weightings vary with position in the space. A rotation term also corrects the behaviour in the blue region. Weights vary with position throughout the space. CIELAB non-uniformity is what they correct.
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Match each CIEDE2000 term with what it corrects.
List I
A. Lightness weighting
B. Chroma weighting
C. Hue weighting
D. Rotation term
List II
1. variation of tolerance around the hue circle
2. variation of tolerance with lightness
3. the anomalous behaviour in the blue region
4. larger tolerances at high chroma
Answer: C
Each was fitted to experimental visual difference data. The formula is considerably more elaborate than the Euclidean distance it replaced. Each term was fitted to visual difference data. The formula is elaborate by necessity.
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Assertion (A): CIEDE2000 includes a rotation term acting mainly in the blues.
Reason (R): Visual data showed the difference ellipses tilted in that region of the space.
Answer: D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. The visual data used to fit CIEDE2000 showed the difference ellipses in the blue region tilted rather than aligned with the chroma and hue axes, which no combination of separate weighting functions could represent. The rotation term was introduced to account for that tilt, and it acts almost entirely in the blues.
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