Raju Shrestha

Eigensteps: A giant leap for gait recognition

In this paper we will show that using Principle Component Analysis (PCA) on accelerometer based gait data will give a large improvement on the performance. On a dataset of 720 gait samples (60 volunteers and 12 gait samples per volunteer) we achieved an EER of 1.6% while the best result so far, using the Average Cycle Method (ACM), gave a result of nearly 6%. This tremendous increase makes gait recognition a viable method in commercial applications in the near future.

Spatial Arrangement of Color Filter Array for Multispectral Image Acquisition

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 imaging using a stereo camera: concept, design and assessment

This paper proposes a one-shot six-channel multispectral color image acquisition system using a stereo camera and a pair of optical filters. The two filters from the best pair, selected from among readily available filters such that they modify the sensitivities of the two cameras in such a way that they produce optimal estimation of spectral reflectance and/or color, are placed in front of the two lenses of the stereo camera. The two images acquired from the stereo camera are then registered for pixel-to-pixel correspondence. The spectral reflectance and/or color at each pixel on the scene are estimated from the corresponding camera outputs in the two images. Both simulations and experiments have shown that the proposed system performs well both spectrally and colorimetrically. Since it acquires the multispectral images in one shot, the proposed system can solve the limitations of slow and complex acquisition process, and costliness of the state of the art multispectral imaging systems, leading to its possible uses in widespread applications.

LED Based Multispectral Film Scanner for Accurate Color Imaging

LED (Light Emitting Diode) based spectral imaging is advantageous for its fast computer controlled switching ability, availability of many different types of LEDs and cost effectiveness. It has been used in some applications like biometrics and arts, however, it has not been explored in film scanning. Here in this paper, we have proposed a LED based spectral film scanner that allows acquiring spectral data and at the same time producing more accurate digital color images. Such a system, in practice, is constrained by the limit in the number of LEDs to be used. We have studied the performance of the system also, under the influence of the number of LEDs. Simulation experiments show that the system is capable of acquiring accurate color images with a fairly reasonable number of LEDs. We have also investigated the influence of noise on the number of LEDs, and it shows that the noise plays some part on the number of LEDs to be used.

Simultaneous multispectral imaging and illuminant estimation using a stereo camera

We propose here a novel approach to acquire a multispectral image and at the same time estimate the illuminant with the use of a stereo camera. Two images of a scene: one normal RGB and one filtered image with an appropriate optical filter selected from among readily available filters placed in front of a lens of the stereo camera are acquired. The spectral reflectance and/or color at each pixel on the scene are estimated from the corresponding outputs in the two images. In the mean time, the illuminant used during the image capture is estimated using chromagenic illuminant estimation method. Experiments with the simulated data show that this is a promising technique for simultaneous multispectral imaging and the illuminant estimation. Todays increasing commercial availability of digital stereo cameras makes the proposed solution a viable one for many applications.

CFA based simultaneous multispectral imaging and illuminant estimation

This paper proposes an extension to the CFA based multispectral imaging with an added capability of illuminant estimation. A special filter is used on top of regular R, G and B filters of a camera, replacing one of the two green filters, with one of them. This gives a six channel multispectral image. A normal RGB image is produced by the RGB filters. The corresponding filtered RGB image is obtained using the filtered RGB channels. The two images of a scene allow estimating the illuminant using the chromagenic illuminant estimation algorithm. The proposed system is thus capable of acquiring not only multispectral image but also normal RGB image, and at the same time capable of estimating the illuminant under which the image is captured. This makes the system useful in many applications in color imaging and computer vision. Simulation experiments confirm the effectiveness of the proposed system.

Spectrogenic imaging: A novel approach to multispectral imaging in an uncontrolled environment

Increasing the number of imaging channels beyond the conventional three has been shown to be beneficial for a wide range of applications. However, it is mostly limited to imaging in a controlled environment, where the capture environment (illuminant) is known a priori. We propose here a novel system and methodology for multispectral imaging in an uncontrolled environment. Two images of a scene, a normal RGB and a filtered RGB are captured. The illuminant under which an image is captured is estimated using a chromagenic based algorithm, and the multispectral system is calibrated automatically using the estimated illuminant. A 6-band multispectral image of a scene is obtained from the two RGB images. The spectral reflectances of the scene are then estimated using an appropriate spectral estimation method. The proposed concept and methodology is generic one, as it is valid in whatever way we acquire the two images of a scene. A system that can acquire two images of a scene can be realized, for instance in two shots using a digital camera and a filter, or in a single shot using a stereo camera, or a custom color filter array design. Simulation experiments using a stereo camera based system confirms the effectiveness of the proposed method. This could be useful in many imaging applications and computer vision.

How Are LED Illumination Based Multispectral Imaging Systems Influenced by Different Factors

LED illumination based multispectral imaging (LEDMSI) is one of the promising techniques of fast and effective spectral image acquisition. Several LEDMSI systems and methodologies have been proposed in the literature. A typical LEDMSI system uses a monochrome camera, which captures images of a scene under n different color LED lights, producing an n-band spectral image of the scene. RGB camera based LEDMSI systems have been proposed to speed up the acquisition process. However, demosaicing process in these systems affects the spatial accuracy, and in turn influences the quality of resulting spectral images. In this paper, we study how the performance and quality of LEDMSI systems are influenced by different factors. Four major factors: camera type, demosaicing, number of color LEDs and, noise are considered in the study. We carry out simulation experiments using monochrome and RGB camera based LEDMSI systems, under the influence of different amounts of noise and practical constraints on the number of different color LEDs. The experiments confirm the influence of these factors on the performance of a LEDMSI system. We believe that this work would be useful not only in designing LEDMSI systems, but also in developing quality framework(s) for the evaluation of spectral images and spectral imaging systems.

Computational color constancy using chromagenic filters in color filter arrays

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 Bayers 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.

Multispectral imaging: an application to density measurement of photographic paper in the manufacturing process control

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.