Optical properties Quality Characteristics of Agricultural Materials
Color Analysis Three major aspects of food acceptance : Color Flavor Texture Color is the most important The product does not look right, consumer never get to judge the other two aspects.
Color Analysis Color is one portion of the input signals to the brain that reacts to produce the perception of appearance. By the eye, color is an interpretation by brain of the character of light coming form an object. But serious limitations when use color measurement as a research or quality control tool. The measurement of color in foods today is a mature science
Physiological Basic of Color The eye has two types of sensitive cells in the retina The rod : lightness and darkness The cones : color Red Green blue
Physiological Basic of Color Visible spectrum (wavelength = 400-760 nm) Ultraviolet < 400 nm Violet 400-450 nm Blue 450-500 nm Green 500-570 nm Yellow 570-590 nm Orange 590-620 nm Red 620-760 nm Infrared >760 nm
Physiological Basic of Color An object is seen as black if it absorbs all colors of white light. A white object reflects all colors of white light. The yellow strip absorbs red, orange, green, blue, indigo and violet light. It reflects yellow light and we see it as yellow.
Physiological Basic of Color The eye also uses complementary colors in color vision. When a color is removed from white light we see the complementary color. The yellow strip in the following figure looks yellow because it absorbs indigo light from white light. Indigo is the complementary color of yellow.
Physiological Basic of Color The following table shows the colors seen when a complementary color is removed. Wavelength Absorbed (nm) Color Absorbed Visual Color 400-430 Violet Lemon Yellow 435-480 Indigo Yellow 480-490 Blue Orange 490-500 Blue-green Red 500-560 Green Purple 560-580 Lemon Yellow Violet 580-595 Yellow Indigo 595-605 Orange Blue 605-750 Red Blue-green
Illuminants A profile or spectrum of visible light which is published in order to allow images or colors recorded under different lighting to be compared. Type of illuminants Illuminant A : tungsten-filament lighting (yellow) Illuminant C : noon sunlight Illuminant D65 : natural daylight
Color system 1.Munsell Color System Created by Professor Albert H. Munsell in 1912 A color space that specifies colors based on three color dimensions, hue, value (lightness), and chroma (color purity or colorfulness).
Hue Color system one of the main properties of a color described with names. Each horizontal circle Munsell divided into Principal hues : Red, Yellow, Green, Blue, and Purple Intermediate hues (5) Second intermediate hues (10) Special intermediate hue (80)
Color system Value Value, or lightness, varies vertically along the color solid, from black at the bottom, to white at the top. 0 = perfect black 1-3 = dark value 4-6 = medium value 7-9 = light value 10 = perfect white
Color system Chroma Chroma represents the purity of a color. Measured radially from the center of each slice
Color system Specifying a color A color is fully specified by listing the three numbers for hue, value, and chroma. hue value/chroma Ex. Color of green bean = GY 5/6 Hue = GY (Green-yellow) Value = 5 Chroma = 6
Color system 2.CIE System CIE = Commission internationale de L Eclairage (1931) The human eye has receptors 3 primaries color spectrum Red (X) 700 nm Green (Y) 520 nm Blue (Z) 400 nm The primaries color can mix up to any color.
Color system The value of each color (R,G,B) from colorimeter are tristimulus. Tristimulus X = Red Tristimulus Y = Green Tristimulus Z = Blue Chromaticity (x,y,z) is an objective specification of the quality of a color regardless of its luminance x = X X+Y+Z y = Y X+Y+Z z = Z X+Y+Z or z = 1- x - y
Color system Chromaticity Diagram of CIE Color System
Color system Specifying a color Ex. The X, Y, Z value of tomato ketchup from colorimeter are 13.0768, 8.8440 and 2.9515 respectively. Haw can report the color of this tomato ketchup in CIE system? x = 13.0768 = 0.5259 24.8723 y = 8.8440 = 0.3553 24.8723 The color of this tomato ketchup in CIE system (x, y, z) is 0.5259, 0.3553 and 0.1188 respectively. z = 2.9515 = 0.1188 24.8723
Color system 0.3553 0.5259 Chromaticity Diagram of CIE Color System
Color system 3.Hunter Color System (Lab) Hunter (1958) was develop this system from CIE system. L (Lightness) = tristimulus Y a = tristimulus X and Y b = tristimulus Z and Y The Hunter L, a, b color space is organized in cube form. L axis run from top to bottom. a and b axis have no specific numerical limits. Positive a is red, negative a is green. Positive b is yellow, negative b is blue.
CIE Convert to Hunter Color System L = 10Y 1/2 a = [17.5 (1.02X - Y)] / Y 1/2 b = [7.0 (Y 0.847z)] / Y 1/2
Color system Hunter L, a, b Color Space Diagram
Color system In Hunter system, E, the color difference between sample and standard can be determined : E L 2 a 2 b 2
Color system 4. CIELAB System L* = 116 (Y/Yn) 1/3 16 for (Y/Yn) 1/3 > 0.008856 L* = 903.3(Y/Yn) 1/3 for (Y/Yn) 1/3 < 0.008856 a* = 500 [(X/Xn) 1/3 (Y/Yn) 1/3 ] = Hue (*h) b* = 200 [(Y/Yn) 1/3 (Z/Zn) 1/3 ] = Chroma (*C) Xn, Yn, Zn = Tristimulus value ของ Reference White ภายใต แหล งกาเน ดแสง หน ง เช น D65 (Yn = 100 เสมอ ส วน X/Xn, Y/Yn และ Z/Zn > 0.01)
Color evaluation Color evaluation can be divided into 2 types : 1. Subjective color evaluation 2. Objective color evaluation
1.Subjective color evaluation Color dictionaries The dictionary of Maerz and Paul Munsell book of color Ridgway charts USDA color standards Macbeth Munsell Disk Colorimetry Tintometer
The dictionary of Maerz and Paul
Munsell book of color
Munsell book Usage
Munsell book Usage
Ridgway charts
USDA color standard
Farnworth Munsell 100 Hue Test
Lovibond tintometer Oil, Fat, Butter etc.
2. Objective color evaluation Spectral reflectance meter
Hunter colorimeter
Transmittance meters Beer, Vineagar, Honey, Alcohol beverage etc.