Multispectral Imaging of Heritage Artefacts with VideometerLab 3
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The document discusses the capabilities of the VideometerLab 3, which utilizes multi-spectral imaging for rapid and non-destructive surface analysis, enabling the differentiation and quantification of chemical and physical properties of surfaces through statistical image processing. It highlights the advantages over traditional RGB imaging, such as improved spectral resolution and the ability to recognize pigments and details in artworks and historical documents. The technology allows for flexible image analysis with tools designed for both novice and advanced users, contributing to efficient high-throughput data acquisition and compliance archiving.
Multispectral Imaging of Heritage Artefacts with VideometerLab 3
- 1. © analytikLtd analytikLtd VideometerLab 3 Multi-Spectral Imaging Rapid Non-destructive Surface Analysis Adrian Waltho, Analytik Ltd (Cambridge, UK) adrian.waltho@analytik.co.uk www.analytik.co.uk/multispectral-imaging • Light reflectance at separate colours • Statistical image processing • Chemical, physical and spatial properties • Differentiate | Quantify | Report
- 2. © analytikLtd Traditional colour imaging uses three broad bands of colour: Red, Green and Blue Normal Colour Imaging
- 3. © analytikLtd Normal Colour Imaging • RGB photographs have limited spectral resolution • Chlorophyll a and b give almost the same RGB signal and are not spectrally separated Chloro-a High Low High Chloro-b High Low High
- 4. © analytikLtd Multispectral Imaging Chloro-a High Low Low High Chloro-b Med High Med Low • Using just 4 wavelength bands with tightly defined ranges, Chlorophyll a and b can easily be distinguished • VideometerLab 3 uses 19 wavelength bands
- 5. © analytikLtd Multispectral Imaging • Many images obtained at selective wavelength bands • Each image pixel contains spectral data points • Spectral signature reveals chemo-specific information • See spatial location of surface chemical variation Ultraviolet Near-Infrared Infra-Red Red Yellow Green Blue Ultra-Violet
- 6. © analytikLtd VideometerLab 3 Schematic • Narrowband illumination provided by 19 LEDs between 375nm-970nm (UV-Vis-VNIR) • Integrating sphere diffuses light onto sample • 2056x2056 CCD camera captures reflectance at each LED wavelength for each pixel • Emission filter wheel for longpass/bandpass filtering • Bright-field or dark-field lighting for translucency or diffuse scatter imaging Camera LEDs Integrating sphere Emission filter wheel Sample
- 7. © analytikLtd VideometerLab 3 Schematic • Precise lighting control for optimal illumination of each sample across whole spectrum • Diffuse light on sample ensures even lighting from all directions • Broadband camera spectrally and spatially calibrated (NIST) • Emission filters enable multispectral reflectance and fluorescence imaging abilities • Powerful, user-friendly image analysis and quantification software for data and modelling Camera LEDs Integrating sphere Emission filter wheel Sample
- 8. © analytikLtd VideometerLab 3 Schematic
- 9. Back to Index Zoom area for next slide Bodleian Library – Papyrus Hieroglyphics
- 10. Back to Index Bodleian Library – Papyrus Hieroglyphics
- 11. Back to Index a at 850nm mination (false note smudge just above tear visible in RGB mage Bodleian Library – Papyrus Hieroglyphics
- 12. Back to Index nCDA transformation of same area
- 13. Back to Index Palimpsest sRGB image Zoom area for next slide
- 14. Back to Index Close-up of zoomed area
- 15. Back to Index nCDA transform highlights original text
- 16. © analytikLtd Historic Scotland – Pigment analysis Back to Index • Circled are cadmium red and lead white pigment samples
- 17. © analytikLtd Back to Index • Circled is a mix of cadmium red and lead white Historic Scotland – Pigment analysis
- 18. © analytikLtd Back to Index • The VideometerLab can build up a library of the spectral responses of each pigment Historic Scotland – Pigment analysis
- 19. © analytikLtd Back to Index • The VideometerLab can then recognise this spectrum in unknown samples. We see that the pure cadmium red and the cadmium red mix are both ‘hits’ for the cadmium spectrum Historic Scotland – Pigment analysis
- 20. © analytikLtd Back to Index • We can also see that the more pure spectrum registers as a closer fit than the cadmium-lead mix. We see this because the pure cadmium is much more orangey in the false-colour image Historic Scotland – Pigment analysis
- 21. © analytikLtd Back to Index • This technique can be applied to paintings, for example this portrait of a captain from Leith Historic Scotland – Pigment analysis
- 22. © analytikLtd Back to Index • By using false-colouration, we can see that the yellow pigment used on the captain’s hatband is the same (or very similar) to the yellow on his buttons, but different from the yellow on his braiding Historic Scotland – Pigment analysis
- 23. © analytikLtd Royal Armouries Fencing Manual Back to Index20
- 24. © analytikLtd Royal Armouries Fencing Manual Back to Index20
- 25. © analytikLtd This image shows the redness on the left fighter’s cheek is spectrally the same as the scribbling in the middle of the picture and the spot in the bottom left Perhaps more importantly, it shows there is nothing else of a similar pigmentation in the whole image Back to Index21 Royal Armouries Fencing Manual
- 26. © analytikLtd This image shows the redness on the left fighter’s cheek is spectrally the same as the scribbling in the middle of the picture and the spot in the bottom left Back to Index22 Royal Armouries Fencing Manual
- 27. © analytikLtd The Videometer can prove this quantitatively as well – the next slide shows the spectral properties of the points in the center of the small crosses below Back to Index24 Royal Armouries Fencing Manual
- 28. © analytikLtd You can see that 3 and 4 (teal and brown, page and sword) are significantly different from 1 and 2 in terms of their spectral profile. Back to Index25 Royal Armouries Fencing Manual
- 29. © analytikLtd Visually, the Sten gun looks scratched arbitrarily. In fact, it is known there is an engraving on the side Royal Armouries Sten Gun Back to Index8
- 30. © analytikLtd The Videometer can isolate an blow up this engraving Back to Index9 Royal Armouries Sten Gun
- 31. © analytikLtd The Videometer can also spectrally enhance the contrast Back to Index10 Royal Armouries Sten Gun
- 32. © analytikLtd Ordinary RGB imaging cannot do this - it is only possible to get the clarity of the enhanced image at 850 nanometers where the scratches start to respond differently to the metal under illumination, and RGB cameras only go up to around 700nm Back to Index1 Royal Armouries Sten Gun
- 33. © analytikLtd The Videometer can false-colour images to aid understanding Back to Index12 Royal Armouries Sten Gun
- 34. © analytikLtd It can also focus tightly on specific sections of the image to contrast them better – it is possible to improve signal to noise almost without limit at the expense of spending more time on the analysis Back to Index13 Royal Armouries Sten Gun
- 35. © analytikLtd ΧΡΙΣΤΗΦΗΣ ΗΛΙΑ “Christofis Elias” Royal Armouries Sten Gun
- 36. © analytikLtd ΛΟΧΟΣ ΣΤ “Sixth Company” Royal Armouries Sten Gun
- 37. © analytikLtd ΛΕΥΚΩΣΙΑ “Lefkosia” Royal Armouries Sten Gun
- 38. © analytikLtd • The gun belonged to a Greek Cypriot named Elias Christofis who fought in World War II. (Lefkosia is the capital of Cyprus) • Some of the decisions between similar looking letters might appear odd, but make a lot of sense when looked at multi- spectrally: – For example, this letter looks like it could easily be a lambda or an aleph, but when viewed at 920 rather than 850nm, the line in the middle disappears Back to Index17 Royal Armouries Sten Gun
- 39. © analytikLtd • The translations were done by a Greek-speaker, who said that the transliteration of the third line that was given to her didn’t make sense. Its unclear if that means what Mr Christofis wrote was literally nonsense or if I transliterated it badly, but I would guess the latter • This could be solved by a more guided transformation process – for example taking a more careful image of the third section of writing, finding out more about the sample so you can ‘guess’ letters and have the Videometer fill in the blanks or by a more complicated transformation calibration Back to Index18 Royal Armouries Sten Gun
- 40. © analytikLtd Museum Conservation Service • Faded ‘Elizabeth R’ signature on official declaration of war communication document to overseas UK forces (sRGB image)
- 41. © analytikLtd • Faded ‘Elizabeth R’ signature on official declaration of war communication document to overseas UK forces (sRGB image) • Highlight training set of pixels to teach the software the spectral pattern of interest Museum Conservation Service Yes No
- 42. © analytikLtd • Faded ‘Elizabeth R’ signature on official declaration of war communication document to overseas UK forces • Highlight training set of pixels to teach the software the spectral pattern of interest • Software scores every pixel in the image using the trained nCDA algorithm • nCDA score determines pixel false colour value • Signature’s spectrum is highlighted against all other dis- similar spectra on the page Museum Conservation Service
- 43. © analytikLtd Museum Conservation Service • Faded Officer’s co-signature on official declaration of war communication document to overseas UK forces (sRGB image)
- 44. © analytikLtd Museum Conservation Service • Faded Officer’s co-signature on official declaration of war communication document to overseas UK forces (sRGB image) • Highlight training set of pixels to teach the software the spectral pattern of interest Yes No
- 45. © analytikLtd Museum Conservation Service • Faded Officer’s co-signature on official declaration of war communication document to overseas UK forces • Highlight training set of pixels to teach the software the spectral pattern of interest • Software scores every pixel in the image using the trained nCDA algorithm • nCDA score determines pixel false colour value • Signature’s spectrum is highlighted against all other dis- similar spectra on the page
- 46. © analytikLtd Museum Conservation Service • Faded pencil inscription on the rear of a photograph of unknown British officer in 1858 (sRGB image, date circled) • Highlight training set of pixels to teach the software the spectral pattern of interest ‘1858’ written in pencil
- 47. © analytikLtd Museum Conservation Service • Faded pencil inscription on the rear of a photograph of unknown British officer in 1858 • Highlight training set of pixels to teach the software the spectral pattern of interest • Software scores every pixel in the image using the trained nCDA algorithm • nCDA score determines pixel false colour value • Pencil spectrum is highlighted against all other dis-similar spectra on the page
- 48. © analytikLtd Museum Conservation Service • Suspected signature painted over in final composition • Almost invisible in sRGB image
- 49. © analytikLtd Museum Conservation Service • Suspected signature painted over in final composition • Almost invisible in sRGB image • Highlight training set of pixels to teach the software the spectral pattern of interest
- 50. © analytikLtd Museum Conservation Service • Suspected signature painted over in final composition • Almost invisible in sRGB image • Highlight training set of pixels to teach the software the spectral pattern of interest • Software scores every pixel in the image using the trained nCDA algorithm • nCDA score determines pixel false colour value • Signature’s spectrum is highlighted against all other dis- similar spectra on the page
- 51. © analytikLtd Multispectral Image Analysis • A variety of image processing tools are available in VideometerLab’s analysis software • Analysis protocols and models can be saved and applied to new samples for routine analysis • Multiple analysis models can be run on the same image data to quantify separate parameters • Analysis can be batch-run to aid in high-throughput data acquisition • Image archiving provides a record of samples for future data mining and regulatory compliance
- 52. © analytikLtd • Nuanced, human-like analysis of heterogeneous samples • Objective, accurate, repeatable measurements • Non-destructive analysis allows further sample assay work • No sample preparation is required • Rapid data acquisition and analysis enables high throughput screening Why use Multispectral Imaging?
- 53. © analytikLtd • Hardware options • Emission filter wheel (4 x 25mm Ø) for fluorescence macro-imaging • Dark- or Bright-field backlighting for scattering or translucency analysis • Bespoke solutions available • Software options • Image Processing Toolbox for filtering and segmentation of image data in individual spectral bands • Multispectral Imaging Toolbox for multivariate image analysis and modelling • Blob Toolbox for granular object separation, analysis and data output reporting • Matlab multispectral imaging toolbox integration Hardware and Software Options
- 54. © analytikLtd • Nuanced, human-like analysis of heterogeneous samples • Sophisticated data analysis tools for the novice and power user • Objective, repeatable data collection with easy export • Rapid, non-destructive testing with no sample preparation VL3 Multispectral Imaging adrian.waltho@analytik.co.uk Multispectral imaging at Analytik.co.uk VL3 Datasheet PDF