In this paper, we present an industrial application of multispectral imaging, for density measurement of colorants in photographic
paper. We designed and developed a 9-band LED illumination based multispectral imaging system specifically for
this application in collaboration with FUJIFILM Manufacturing Europe B.V., Tilburg, Netherlands. Unlike a densitometer,
which is a spot density measurement device, the proposed system enables fast density measurement in a large area of a
photo paper. Densities of the four colorants (CMYK) at every surface point in an image are calculated from the spectral
reflectance image. Fast density measurements facilitate automatic monitoring of density changes (which is proportional to
thickness changes), which helps control the manufacturing process for quality and consistent output. Experimental results
confirm the effectiveness of the proposed system.
We have proposed, in this paper, a new color constancy technique, an extension to the chromagenic color constancy.
Chromagenic based illuminant estimation methods take two shots of a scene, one without and one with a specially chosen
color filter in front of the camera lens. Here, we introduce chromagenic filters into the color filter array itself by placing
them on top of R, G or B filters and replacing one of the two green filters in the Bayer's pattern with them. This allows
obtaining two images of the same scene via demosaicking: a normal RGB image, and a chromagenic image, equivalent
of RGB image with a chromagenic filter. The illuminant can then be estimated using chromagenic based illumination
estimation algorithms. The method, we named as CFA based chromagenic color constancy (or 4C in short), therefore,
does not require two shots and no registration issues involved unlike as in the other chromagenic based color constancy
algorithms, making it more practical and useful computational color constancy method in many applications.
Experiments show that the proposed color filter array based chromagenic color constancy method produces comparable
results with the chromagenic color constancy without interpolation.
In the past few years there has been a significant volume of research work carried out in the field of multispectral image
acquisition. The focus of most of these has been to facilitate a type of multispectral image acquisition systems that
usually requires multiple subsequent shots (e.g. systems based on filter wheels, liquid crystal tunable filters, or active
lighting). Recently, an alternative approach for one-shot multispectral image acquisition has been proposed; based on an
extension of the color filter array (CFA) standard to produce more than three channels. We can thus introduce the concept
of multispectral color filter array (MCFA). But this field has not been much explored, particularly little focus has been
given in developing systems which focuses on the reconstruction of scene spectral reflectance.
In this paper, we have explored how the spatial arrangement of multispectral color filter array affects the acquisition
accuracy with the construction of MCFAs of different sizes. We have simulated acquisitions of several spectral scenes
using different number of filters/channels, and compared the results with those obtained by the conventional regular MCFA
arrangement, evaluating the precision of the reconstructed scene spectral reflectance in terms of spectral RMS error, and
colorimetric ▵E*ab color differences. It has been found that the precision and the the quality of the reconstructed images
are significantly influenced by the spatial arrangement of the MCFA and the effect will be more and more prominent with
the increase in the number of channels. We believe that MCFA-based systems can be a viable alternative for affordable
acquisition of multispectral color images, in particular for applications where spatial resolution can be traded off for spectral
resolution. We have shown that the spatial arrangement of the array is an important design issue.
Multispectral color imaging is a promising technology, which can solve many of the problems of traditional RGB color
imaging. However, it still lacks widespread and general use because of its limitations. State of the art multispectral imaging
systems need multiple shots making it not only slower but also incapable of capturing scenes in motion. Moreover, the
systems are mostly costly and complex to operate. The purpose of the work described in this paper is to propose a one-shot
six-channel multispectral color image acquisition system using a stereo camera or a pair of cameras in a stereoscopic
configuration, and a pair of optical filters. The best pair of filters is selected from among readily available filters such
that they modify the sensitivities of the two cameras in such a way that they get spread reasonably well throughout the
visible spectrum and gives optimal reconstruction of spectral reflectance and/or color. As the cameras are in a stereoscopic
configuration, the system is capable of acquiring 3D images as well, and stereo matching algorithms provide a solution to
the image alignment problem. Thus the system can be used as a "two-in-one" multispectral-stereo system. However, this
paper mainly focuses on the multispectral part. Both simulations and experiments have shown that the proposed system
performs well spectrally and colorimetrically.
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