Multispectral Imaging Development at ENST (original) (raw)

Multispectral imaging for computer vision

2018

The main objective of this report is to provide an overview on my research activities on multispectral imaging based on spectral lter arrays. Based on this experience, we formulate future directions and challenges.

Multispectral camera as spatio-spectrophotometer under uncontrolled illumination

Optics Express, 2019

Multispectral constancy enables the illuminant invariant representation of multispectral data. This article proposes an experimental investigation of multispectral constancy through the use of multispectral camera as a spectrophotometer for the reconstruction of surface reflectance. Three images with varying illuminations are captured and the spectra of material surfaces is reconstructed. The acquired images are transformed into canonical representation through the use of diagonal transform and spectral adaptation transform. Experimental results show that use of multispectral constancy is beneficial for both filter-wheel and snapshot multispectral cameras. The proposed concept is robust to errors in illuminant estimation and is able to perform well with linear spectral reconstruction method. This work makes us one step closer to the use of multispectral imaging for computer vision.

Multispectral Imaging Using Multiplexed Illumination

2007 IEEE 11th International Conference on Computer Vision, 2007

Many vision tasks such as scene segmentation, or the recognition of materials within a scene, become considerably easier when it is possible to measure the spectral reflectance of scene surfaces. In this paper, we present an efficient and robust approach for recovering spectral reflectance in a scene that combines the advantages of using multiple spectral sources and a multispectral camera. We have implemented a system based on this approach using a cluster of light sources with different spectra to illuminate the scene and a conventional RGB camera to acquire images. Rather than sequentially activating the sources, we have developed a novel technique to determine the optimal multiplexing sequence of spectral sources so as to minimize the number of acquired images. We use our recovered spectral measurements to recover the continuous spectral reflectance for each scene point by using a linear model for spectral reflectance. Our imaging system can produce multispectral videos of scenes at 30fps. We demonstrate the effectiveness of our system through extensive evaluation. As a demonstration, we present the results of applying data recovered by our system to material segmentation and spectral relighting.

Multispectral and Hyperspectral Imaging

The Encyclopedia of Archaeological Sciences, 2018

Since the invention of photography, a variety of approaches have made noninvasive imaging for cultural heritage applications possible. Multi‐ and hyperspectral imaging (together denoted spectral imaging) are two techniques that evolved from conventional color photography, having overcome its spectral limitations. Instead of imaging in three broad spectral bands, multispectral imaging acquires data in up to ten more or less equally wide and nonoverlapping spectral bands. Hyperspectral imaging goes beyond the multispectral approach by generating images in tens to hundreds of narrow, contiguous (i.e., adjacent but not overlapping) spectral bands. Most spectral imaging techniques are limited to the optical electromagnetic spectrum and acquire the reflected portion of the radiation that is used to illuminate the scene. However, imaging the emitted thermal radiation or active techniques based on laser scanners do exist as well. In cultural heritage, all these techniques are used to gain a better, noninvasive insight into the chemical and physical properties of the object(s) under investigation.

Multispectral system for reflectance reconstruction in the near-infrared region

Applied Optics, 2006

We analyze the performance of a multispectral system that works in the near-infrared (NIR) region of the electromagnetic spectrum (NIR: 800-1000 nm). The system, which uses a CCD camera as a sensor with five acquisition channels, is capable of reconstructing the NIR spectral reflectance curves for a wide range of samples with a high degree of accuracy. We carried out a study of the sources of error in the experimental system, developed a luminance adaptation model to remove the dependence of the captured images on the exposure time of the camera and the f-number of the objective lens, and performed reconstructions of the spectral reflectances of a set of 80 samples. We achieved the best results by using a 12-bit camera, considering a different luminance adaptation transform for each channel, and by using the pseudoinverse reconstruction method. Under these conditions, the system provided mean percentages of reconstruction higher than 99.8% and root-mean-square-error values lower than 0.17, and is therefore suitable for use as a spectrophotometric instrument.

Color and Multispectral Imaging with the CRISATEL Multispectral System

PICS, 2003

We present a first evaluation of the prototype multispectral camera developed in the framework of the IST-CRISATEL European project. This evaluation corresponds to the characterization of the filter transmittances, the CCD properties and the dark noise. We also show the importance of chromatic aberration correction for high resolution multispectral imaging systems.

Recovering spectral information using digital camera systems

Coloration technology, 2001

There is an increasing need to be able to measure colour properties of complex surfaces or images for which traditional spectrophotometers are not suitable. New multispectral imaging systems are being developed but it is not clearly understood how the parameters (such as the number of colour channels, the spectral properties of the channels, and the choice of illuminant) of such systems affect the performance. Furthermore, the effect of sensor and quantisation noise on the overall performance of the system also needs to be considered. This paper describes the development of a mathematical model of a multispectral imaging system that takes into account imaging parameters and noise. The results from the computational model show that increasing the number of colour channels alone in the imaging system does not necessarily allow better estimates of spectral reflectance. The choice of illumination can also, in the presence of noise, greatly affect performance.

Article Multispectral Filter Arrays: Recent Advances and Practical Implementation

2014

Thanks to some technical progress in interferencefilter design based on different technologies, we can finally successfully implement the concept of multispectral filter array-based sensors. This article provides the relevant state-of-the-art for multispectral imaging systems and presents the characteristics of the elements of our multispectral sensor as a case study. The spectral characteristics are based on two different spatial arrangements that distribute eight different bandpass filters in the visible and near-infrared area of the spectrum. We demonstrate that the system is viable and evaluate its performance through sensor spectral simulation.

Multispectral Filter Arrays: Recent Advances and Practical Implementation

Sensors, 2014

Thanks to some technical progress in interferencefilter design based on different technologies, we can finally successfully implement the concept of multispectral filter array-based sensors. This article provides the relevant state-of-the-art for multispectral imaging systems and presents the characteristics of the elements of our multispectral sensor as a case study. The spectral characteristics are based on two different spatial arrangements that distribute eight different bandpass filters in the visible and near-infrared area of the spectrum. We demonstrate that the system is viable and evaluate its performance through sensor spectral simulation.