Optical properties. Quality Characteristics of Agricultural Materials

Transcription

1 Optical properties Quality Characteristics of Agricultural Materials

2 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.

3 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

4 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

5 Physiological Basic of Color Visible spectrum (wavelength = nm) Ultraviolet < 400 nm Violet nm Blue nm Green nm Yellow nm Orange nm Red nm Infrared >760 nm

6 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.

7 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.

8 Physiological Basic of Color The following table shows the colors seen when a complementary color is removed. Wavelength Absorbed (nm) Color Absorbed Visual Color Violet Lemon Yellow Indigo Yellow Blue Orange Blue-green Red Green Purple Lemon Yellow Violet Yellow Indigo Orange Blue Red Blue-green

9 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

10 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).

11 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)

12 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

13 Color system Chroma Chroma represents the purity of a color. Measured radially from the center of each slice

14 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

15 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.

16 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

17 Color system Chromaticity Diagram of CIE Color System

18

19 Color system Specifying a color Ex. The X, Y, Z value of tomato ketchup from colorimeter are , and respectively. Haw can report the color of this tomato ketchup in CIE system? x = = y = = The color of this tomato ketchup in CIE system (x, y, z) is , and respectively. z = =

20 Color system Chromaticity Diagram of CIE Color System

21 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.

22 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

23 Color system Hunter L, a, b Color Space Diagram

24 Color system In Hunter system, E, the color difference between sample and standard can be determined : E L 2 a 2 b 2

25 Color system 4. CIELAB System L* = 116 (Y/Yn) 1/3 16 for (Y/Yn) 1/3 > L* = 903.3(Y/Yn) 1/3 for (Y/Yn) 1/3 < 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)

26

27 Color evaluation Color evaluation can be divided into 2 types : 1. Subjective color evaluation 2. Objective color evaluation

28 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

29 The dictionary of Maerz and Paul

30 Munsell book of color

31 Munsell book Usage

32 Munsell book Usage

33 Ridgway charts

34 USDA color standard

35 Farnworth Munsell 100 Hue Test

36 Lovibond tintometer Oil, Fat, Butter etc.

37 2. Objective color evaluation Spectral reflectance meter

38 Hunter colorimeter

39 Transmittance meters Beer, Vineagar, Honey, Alcohol beverage etc.

40

41