## Compact camera for multispectral and conventional imaging based on patterned filters |

Applied Optics, Vol. 53, Issue 13, pp. C64-C71 (2014)

http://dx.doi.org/10.1364/AO.53.000C64

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### Abstract

A multispectral camera concept is presented. The concept is based on using a patterned filter in the focal plane, combined with scanning of the field of view. The filter layout has stripes of different bandpass filters extending orthogonally to the scan direction. The pattern of filter stripes is such that all bands are sampled multiple times, while minimizing the total duration of the sampling of a given scene point. As a consequence, the filter needs only a small part of the area of an image sensor. The remaining area can be used for conventional 2D imaging. A demonstrator camera has been built with six bands in the visible and near infrared, as well as a panchromatic 2D imaging capability. Image recording and reconstruction is demonstrated, but the quality of image reconstruction is expected to be a main challenge for systems based on this concept. An important advantage is that the camera can potentially be made very compact, and also low cost. It is shown that under assumptions that are not unreasonable, the proposed camera concept can be much smaller than a conventional imaging spectrometer. In principle, it can be smaller in volume by a factor on the order of several hundred while collecting the same amount of light per multispectral band. This makes the proposed camera concept very interesting for small airborne platforms and other applications requiring compact spectral imagers.

© 2014 Optical Society of America

## 1. Introduction

1. N. Tack, A. Lambrechts, P. Soussan, and L. Haspeslagh, “A compact high-speed and low-cost hyperspectral imager,” Proc. SPIE **8266**, 82660Q (2012). [CrossRef]

3. M. Pisani and M. Zucco, “Compact imaging spectrometer combining Fourier transform spectroscopy with a Fabry–Perot interferometer,” Opt. Express **17**, 8319–8331 (2009). [CrossRef]

4. D. B. Cavanaugh, J. M. Lorenz, N. Unwin, M. Dombrowski, and P. Wilson, “VNIR hypersensor camera system,” Proc. SPIE **7457**, 745700 (2009). [CrossRef]

5. A. M. Mika, “Linear-wedge spectrometer,” Proc. SPIE **1298**, 127–131 (1990). [CrossRef]

6. P. Mouroulis, R. O. Green, and T. G. Chrien, “Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information,” Appl. Opt. **39**, 2210–2220 (2000). [CrossRef]

7. T. Skauli, “An upper-bound metric for characterizing spectral and spatial coregistration errors in spectral imaging,” Opt. Express **20**, 918–933 (2012). [CrossRef]

## 2. Camera Concept

6. P. Mouroulis, R. O. Green, and T. G. Chrien, “Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information,” Appl. Opt. **39**, 2210–2220 (2000). [CrossRef]

7. T. Skauli, “An upper-bound metric for characterizing spectral and spatial coregistration errors in spectral imaging,” Opt. Express **20**, 918–933 (2012). [CrossRef]

## 3. Experimental Realization

11. I. Kåsen, A. Rødningsby, T. V. Haavardsholm, and T. Skauli, “Band selection for hyperspectral target-detection based on a multinormal mixture anomaly detection algorithm,” Proc. SPIE **6966**, 696606 (2008). [CrossRef]

## 4. Angle Dependence of Filter Characteristics

## 5. Light Collection and Camera Size

13. T. Skauli, R. Ingebrigtsen, and I. Kåsen, “Effect of light level and photon noise on hyperspectral target detection performance,” Proc. SPIE **6661**, 66610D (2007). [CrossRef]

## 6. Preliminary Imaging Results

## 7. Discussion and Conclusions

## References

1. | N. Tack, A. Lambrechts, P. Soussan, and L. Haspeslagh, “A compact high-speed and low-cost hyperspectral imager,” Proc. SPIE |

2. | H. Saari, V.-V. Aallos, C. Holmlund, J. Mäkynen, B. Delauré, K. Nackaerts, and B. Michiels, “Novel hyperspectral imager for lightweight UAVs,” Proc. SPIE |

3. | M. Pisani and M. Zucco, “Compact imaging spectrometer combining Fourier transform spectroscopy with a Fabry–Perot interferometer,” Opt. Express |

4. | D. B. Cavanaugh, J. M. Lorenz, N. Unwin, M. Dombrowski, and P. Wilson, “VNIR hypersensor camera system,” Proc. SPIE |

5. | A. M. Mika, “Linear-wedge spectrometer,” Proc. SPIE |

6. | P. Mouroulis, R. O. Green, and T. G. Chrien, “Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information,” Appl. Opt. |

7. | T. Skauli, “An upper-bound metric for characterizing spectral and spatial coregistration errors in spectral imaging,” Opt. Express |

8. | X. Sun, “Computerized component variable interference filter imaging spectrometer system method and apparatus,” U.S. patent6,211,906 (3April2001). |

9. | J. Biesemans, B. Delaure, and B. Michiels, “Geometric referencing of multi-spectral data,” Patent application EP2513599 A1 (2012). |

10. | T. Skauli, “Imaging unit,” Patent application NO20130382 (2013). |

11. | I. Kåsen, A. Rødningsby, T. V. Haavardsholm, and T. Skauli, “Band selection for hyperspectral target-detection based on a multinormal mixture anomaly detection algorithm,” Proc. SPIE |

12. | W. J. Smith, |

13. | T. Skauli, R. Ingebrigtsen, and I. Kåsen, “Effect of light level and photon noise on hyperspectral target detection performance,” Proc. SPIE |

14. | R. Harley and A. Zisserman, |

**OCIS Codes**

(040.1490) Detectors : Cameras

(120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors

(100.4145) Image processing : Motion, hyperspectral image processing

(110.4234) Imaging systems : Multispectral and hyperspectral imaging

**History**

Original Manuscript: January 7, 2014

Revised Manuscript: March 25, 2014

Manuscript Accepted: March 26, 2014

Published: April 21, 2014

**Citation**

Torbjørn Skauli, Hans Erling Torkildsen, Stephane Nicolas, Thomas Opsahl, Trym Haavardsholm, Ingebjørg Kåsen, and Atle Rognmo, "Compact camera for multispectral and conventional imaging based on patterned filters," Appl. Opt. **53**, C64-C71 (2014)

http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-53-13-C64

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### References

- N. Tack, A. Lambrechts, P. Soussan, and L. Haspeslagh, “A compact high-speed and low-cost hyperspectral imager,” Proc. SPIE 8266, 82660Q (2012). [CrossRef]
- H. Saari, V.-V. Aallos, C. Holmlund, J. Mäkynen, B. Delauré, K. Nackaerts, and B. Michiels, “Novel hyperspectral imager for lightweight UAVs,” Proc. SPIE 7668, 766805 (2010). [CrossRef]
- M. Pisani and M. Zucco, “Compact imaging spectrometer combining Fourier transform spectroscopy with a Fabry–Perot interferometer,” Opt. Express 17, 8319–8331 (2009). [CrossRef]
- D. B. Cavanaugh, J. M. Lorenz, N. Unwin, M. Dombrowski, and P. Wilson, “VNIR hypersensor camera system,” Proc. SPIE 7457, 745700 (2009). [CrossRef]
- A. M. Mika, “Linear-wedge spectrometer,” Proc. SPIE 1298, 127–131 (1990). [CrossRef]
- P. Mouroulis, R. O. Green, and T. G. Chrien, “Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information,” Appl. Opt. 39, 2210–2220 (2000). [CrossRef]
- T. Skauli, “An upper-bound metric for characterizing spectral and spatial coregistration errors in spectral imaging,” Opt. Express 20, 918–933 (2012). [CrossRef]
- X. Sun, “Computerized component variable interference filter imaging spectrometer system method and apparatus,” U.S. patent6,211,906 (3April2001).
- J. Biesemans, B. Delaure, and B. Michiels, “Geometric referencing of multi-spectral data,” Patent application EP2513599 A1 (2012).
- T. Skauli, “Imaging unit,” Patent application NO20130382 (2013).
- I. Kåsen, A. Rødningsby, T. V. Haavardsholm, and T. Skauli, “Band selection for hyperspectral target-detection based on a multinormal mixture anomaly detection algorithm,” Proc. SPIE 6966, 696606 (2008). [CrossRef]
- W. J. Smith, Modern Optical Engineering, 3rd ed. (McGraw-Hill, 2000), p. 208.
- T. Skauli, R. Ingebrigtsen, and I. Kåsen, “Effect of light level and photon noise on hyperspectral target detection performance,” Proc. SPIE 6661, 66610D (2007). [CrossRef]
- R. Harley and A. Zisserman, Multiple View Geometry in Computer Vision, 2nd ed. (Cambridge University, 2003).

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