Hyperspectral Image capture and analysis of The Scream (1893)

Transcription

1 Hyperspectral Image capture and analysis of The Scream (1893) Ferdinand Deger, Sony Georg, Jon Y. Hardeberg

2 Hyperspectral Imaging

3 Acquisition of The Scream National museum in Oslo: Trond Aslaksby (Restorer) Børre Høstland (Photographer) Andreas Harvik (Photographer) Norsk Elektro Optikk: Ivar Baarstad Julio Ernesto Hernandez Palacios Trond Løke Gjøvik University College: Jon Yngve Hardeberg (Professor) Sony George (Post-Doc) Ferdinand Deger (PhD-student) Université de Bourgogne: C2RMF: Alamin Mansouri Ruven Pillay 2

4 Two Hyperspectral Cameras Detector SSi CCD 1600 x 1200 Spectral range µm Spatial pixels 1600 FOV across track 17 Pixel FOV across/- along track* Spectral sampl mrad/ 0.36 mrad 3.7 nm # of bands 160 Binning modes 2, 4, 8 Digitization Max frame rate VNIR 1600 Sensor head wgt. Sensor head dim. (lwh in cm) Sensor head pwr. consumption Camera interface 12 bit 135 fps 4.6 kg 31.5x8.4x13.8 ~6 W Camera Link Detector HgCdTe 320 x 256 Spectral range µm Spatial pixels 320 FOV across track 13.5 Pixel FOV across/- along track Spectral sampl mrad/ 0.75 mrad 6 nm # of bands 256 Digitization Max frame rate* Sensor head wgt. Sensor head dim. (lwh in cm) Sensor head pwr. consumption Camera interface SWIR 320m-e 14 bit 100 fps 7.5 kg 36x14x15.2 ~100 W Camera Link

5 Acquisition Setup

6 Acquisition Distance Overhead view: Fixed focal length X translation Fixed focal length X translation Spatial resolution of 0.06 mm for focal length of 30 cm Spatial resolution of ~0.2 mm for focal length of 100 cm 5

7 Cross-Polarisation Specularity One Polariser in front the illumination, another in front of the camera Specularities remain polarised and are eliminated from the acquisition Diffuse reflection = Pigments 6

8 Calibration and Data Processing 1. Illumination normalisation 1. Non-uniformity of light + absolute illumination 2. Recover spectral reflectance 2. Geometrical undistortion (more on the next slides) 3. Mosaicking 7

9 Different Pixel Sizes Imaging Spectrometer Users Manual 2 HySpex The HySpex line of hyperspectral cameras is a result of the knowledge and experience accumulated through more than a decade (since 1995) of research activities (initially space and military projects) in the field of imaging spectroscopy at Norsk Elektro Optikk AS. All the spectrometer modules are based on the same general architecture, with optics, sensors and gratings separately optimized for the different modules. 2.1 General design and operating principle Briefly, the camera operates internally as illustrated schematically in Figure 2. The fore optic of the camera (focusing mirror) images the scene onto a slit which only passes light from a narrow line in the scene. After collimation, a dispersive element (in our case a transmission grating) separates the different wavelengths, and the light is then focused onto a detector array. The net effect of the optics is that for each pixel interval along the line defined by the slit, a corresponding spectrum is projected on a column of detectors on the array. The data read out from the array thus contains a slice of a hyperspectral image, with spectral information in one direction and spatial (image) information in the other. 1 2 Focusing mirror Entrance aperture Incoming light Slit spatial Collimating mirror Grating Lens optics Detector Figure 2. Schematic drawing of the HySpex optical system. From HySpex User Manual The HySpex fore-optics and collimating optics is based on a special configuration of two aspherical mirrors. This unique design avoids introduction of spherical and chromatic aberrations before the grating, and at the same time minimizes stray light. The transmission grating is polarization independent and has been chosen among a large selection tested gratings. The lens system for final focus is optimized for minimization and equalization of the point spread function across the FOV and spectral range. Additionally, spectral keystone and smile effects are only a small fraction of a pixel. The spectrometer modules are very rugged with no moving parts, except for the shutter used for dark offset measurements. This document is the property of Norsk Elektro Optikk AS. It may not be copied or disclosed without written consent 8

10 Geometrical undistortion 1. Camera Model of every unit slightly different 2. Inverting the model + Spline interpolation for each pixel

11 VNIR Image We used the cross-polarised version Acquisition Distance 1 m Spatial Resolution ~ 3500x4500 pixel (3 Stripes have been mosaicked ) Spectral Sampling160 bands ~ 3.6 nm

12 SWIR Image Acquisition Distance 30 cm Spatial Resolution ~ 3000x3000 pixel (11 Stripes have been mosaicked ) Spectral Sampling 256 bands ~ 6 nm

13 Correlations

14 Wording in The Scream

15 Simulated illuminations Concord MK41 TH 3000K Cooper DL11WSCW LED Endura OT163101WT LED 6336K 7600 CRI D65 Erco Eclipse Clear Lens TH GE F40WAD FL 6500K 9200CRI GE Par 38 80W Flood_TH

16 Pigment locations considered during previous studies *'Investigation of Materials Used by Edvard Munch';Brian Singer, Trond Aslaksby, Biljana Topalova-Casadiego and Eva Storevik Tveit;Studies in conservation 55 (2010)

17 Thank you for your attention Contact: