it. Reflectance is the ratio between the response of the instrument to
the sample and the response to a known standard, usually a highly
reflective sample [28]. Both transmittance and reflectance are
intrinsic properties of the object, which do not depend on the
illumination received or the observer, in contrast to what occurs
with color. The efficiency, resolution, sensitivity and spectral range
of the spectrophotometers will depend on the design variables and
the selection of the optical components that comprise it [29].
1.4.3
Spectroradiometers
Spectroradiometers typically obtain the radiometric measurement of
the spectral distribution of a primary or secondary radiation source.
As in the case of spectrophotometers, tristimulus values are calculated through mathematical integration. The spectroradiometer has
the same components as the spectrophotometer with the exception
of the light source which, in this case, is external to the instrument
and, therefore, variable. These instruments can also be used to
measure the transmittance or reflectance of any object [26].
All these classic instruments (colorimeters, spectrophotometers
and spectroradiometers) require a certain chromatic uniformity in
the samples so that the measure of the color is representative. This
requirement is sometimes complicated for small samples. In these
cases, the use of digital image analysis (DIA) for the color measurement is highly recommended. An artificial vision device consists
of a lighting system, a device that captures the images and converts
the analogue signal into digital (digital camera), and a computer
with the appropriate software for processing images and interpreting results [30]. In this process, the digital camera receives the
images in its CCD device, which register the color in gradations
of three basic colors: red, green, and blue (RGB), in accordance
with the three-dimensional character of color. Thus, this methodology is based on the acquisition of an image for further analysis,
from which the total color of the object can be obtained. One of the
advantages of this technique is that it can be used to measure not
only the average color, but also the distribution of the color within
the sample. The use of digital cameras in relation to color measurement has been developed and spread widely due to the fidelity in
the measurement and the quality of the image. One of the most
used systems is the DigiEye system [31] consisting of a Nikon D-80
digital camera connected to a controlled lighting camera (VeriVide
DigiEye®, Leicester, UK) and a computer with the DigiPix
software.
1.5 Color
Measurement and
Carotenoid Content
Given the advantages of the instrumental measurements of color, it
is not surprising that it has been long used to rapidly estimate
carotenoid levels in products like citrus fruits carrots or tomatoes,
as typical examples. In this sense, it can be harnessed for different
purposes, including [4]:
Applications of Visible Spectroscopy and Color Measurements in the. . .
109
the sample and the response to a known standard, usually a highly
reflective sample [28]. Both transmittance and reflectance are
intrinsic properties of the object, which do not depend on the
illumination received or the observer, in contrast to what occurs
with color. The efficiency, resolution, sensitivity and spectral range
of the spectrophotometers will depend on the design variables and
the selection of the optical components that comprise it [29].
1.4.3
Spectroradiometers
Spectroradiometers typically obtain the radiometric measurement of
the spectral distribution of a primary or secondary radiation source.
As in the case of spectrophotometers, tristimulus values are calculated through mathematical integration. The spectroradiometer has
the same components as the spectrophotometer with the exception
of the light source which, in this case, is external to the instrument
and, therefore, variable. These instruments can also be used to
measure the transmittance or reflectance of any object [26].
All these classic instruments (colorimeters, spectrophotometers
and spectroradiometers) require a certain chromatic uniformity in
the samples so that the measure of the color is representative. This
requirement is sometimes complicated for small samples. In these
cases, the use of digital image analysis (DIA) for the color measurement is highly recommended. An artificial vision device consists
of a lighting system, a device that captures the images and converts
the analogue signal into digital (digital camera), and a computer
with the appropriate software for processing images and interpreting results [30]. In this process, the digital camera receives the
images in its CCD device, which register the color in gradations
of three basic colors: red, green, and blue (RGB), in accordance
with the three-dimensional character of color. Thus, this methodology is based on the acquisition of an image for further analysis,
from which the total color of the object can be obtained. One of the
advantages of this technique is that it can be used to measure not
only the average color, but also the distribution of the color within
the sample. The use of digital cameras in relation to color measurement has been developed and spread widely due to the fidelity in
the measurement and the quality of the image. One of the most
used systems is the DigiEye system [31] consisting of a Nikon D-80
digital camera connected to a controlled lighting camera (VeriVide
DigiEye®, Leicester, UK) and a computer with the DigiPix
software.
1.5 Color
Measurement and
Carotenoid Content
Given the advantages of the instrumental measurements of color, it
is not surprising that it has been long used to rapidly estimate
carotenoid levels in products like citrus fruits carrots or tomatoes,
as typical examples. In this sense, it can be harnessed for different
purposes, including [4]:
Applications of Visible Spectroscopy and Color Measurements in the. . .
109