Reflectance colour measurement

The in.struinent consists of three main parts. In the first place there is the photometer which measures reflectance at sixteen spectral points. The absorption properties of the dyes at these sixteen wavelengths are stored in dye boxes (Fig. 26.38) and two variables are allowed for each wavelength so that one can make the necessary compensations for the natural colour of the substrate, a factor of increased significance when dyeing pale shades. 

Apart from considering all of the above, it is also important to recognise that sample preparation and presentation may be influenced by the desired resnlt of the colonr measnrement. For example, if the goal is to achieve a good correlation with sensory data, then it is essential that the instmmentally measured sample should be in the same state as that seen by the visual panel. If colour measurement is to be used as a buying criterion the trial sample must be presented as was the standard used to set the tolerance hmits. Also, if a relationship between colour and some other physical parameter is to be made, e.g., particle-size or water-activity, both samples should undergo the same preparation for each test. Some general rules for the preparation of different types of food materials for reflectance colour measurement are discussed as follows. 

The My and hue values are derived from the CIELAB co-ordinate Yn, Xn, Zn and allows a numerical quantification of black jetness. This is only possible with the development of colour measurement equipment that can operate under reflection conditions of less than 1%. (Figure 3). 

Light reflectance (reflectance, reflectivity). The fraction of the total luminous flux incident upon a surface that is reflected, generally a function of the color (wavelength) of the light. Johnson SF (2001) History of hght and colour measurement a science in the shadows. Taylor and Francis, London, UK. Saleh BEA, Teich MC (1991) Fundamentals of photonics. John Wiley and Sons, New York. 

Visible reflectance spectroscopy is used routinely to measure the colour of opaque objects such as textile fabrics, paint films and plastics for purposes such as colour matching and dye and pigment recipe prediction. There is now a wide range of commercially-available reflectance spectrophotometers used industrially as colour measurement devices for such purposes. In many ways, this technique may be considered as complementary to the use of visible absorption spectroscopy for the measurement of transparent dye solutions. Reflectance spectra of typical red, green and blue surfaces... 

Mathematical approaches that make use of concepts associated with colour space for colour measurement and specification based on reflectance spectroscopy have become well-established. Indeed the calculations involved are normally implemented in the software that is provided within an instrument used for colour measurement. The basis of all colour measurement systems is the CIE system of colour specification, which was agreed in 1931. The Commission Internationale de I Eclairage (CIE) is an international organisation promoting cooperation and information exchange on matters relating to the science and art of lighting. An important approach used for the... 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

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