Question

The Hunter Lab system is commonly used for objective colour measurement in foods. The a* value represents

• A. lightness from black to white
• B. red-green axis
• C. blue-yellow axis
• D. glossiness

Hint:

To easily memorize the coordinates:
$L^*$ is for Lightness ($0$ to $100$).
$a^*$ is for Red-Green ($+a^*$ is Red, $-a^*$ is Green).
$b^*$ is for Yellow-Blue ($+b^*$ is Yellow, $-b^*$ is Blue).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the physical definition and representation of the $a^*$ value within the Hunter $L, a, b$ color space system, which is a standard method for objective, non-destructive color measurement in the food industry.

Step 2: Detailed Explanation:

• Color in Food Quality: Color is an important visual quality parameter indicating freshness, degree of cooking, maturity, or degradation. The Hunter Lab system provides a three-dimensional mathematical model to quantify human color perception.

• Opponent-Color Theory: This system is based on the theory that the human brain coordinates vision via three opposing color channels: light-dark, red-green, and yellow-blue.

• The Three Coordinates ($L^*, a^*, b^*$):

• $L^*$ coordinate (Lightness): Ranges from $0$ (representing absolute black) to $100$ (representing absolute white). This matches option (A).

• $a^*$ coordinate (Red-Green axis): Represents chromaticity on the red-green scale. Positive values ($+a^*$) represent redness, whereas negative values ($-a^*$) represent greenness. $0$ is neutral gray. This matches option (B).

• $b^*$ coordinate (Yellow-Blue axis): Represents chromaticity on the yellow-blue scale. Positive values ($+b^*$) represent yellowness, whereas negative values ($-b^*$) represent blueness. This matches option (C).

• Glossiness: This is a surface physical parameter related to specular reflection, which is measured using a glossmeter rather than chromaticity coordinates.

Step 3: Final Answer:
The $a^*$ parameter in the Hunter Lab color scale represents the red-green chromatic axis, making option (B) the correct choice.