CHAPTER-2. Application of Video Spectral Comparator for Examination of Printed Material

Transcription

1 CHAPTER-2 Application of Video Spectral Comparator for Examination of Printed Material

2 2.1 Introduction Historically the document examiner mainly examined handwritten and typed documents. With the evolution in technology the typewriter has almost been replaced by the printers of one sort or another. Spurious documents which relate to one s identity are often produced to support an application for passport, driver s license, bank account or loan, or birth certificate. Sometimes there is a need to identify whether the suspected printer was used to print the fake document or not. Usually the question is whether or not a specific printer or photocopier has produced a particular document. Various printers provide different and valuable evidence based on ink characteristics and individual printer defects which leave some specific wear and tear marks on the paper in the form of striations etc. The various chemical and physical examination can reveal the differences between the printed documents taken from two different printers. Document examination supports the non destructive examination of document so that the document remains intact. Video spectral comparator is one of the versatile instruments which allows non destructive examination of document using multiple instrumental parameters and provides instant results with easier use. The video spectral comparator is an imaging device which allows an examiner to analyze inks, visualize hidden security features, and reveal alterations on a document. VSC works on the basic principles of light. Light is a form of electromagnetic radiation. The visible region is in the range of 400 nm-700 nm in the electromagnetic spectrum. When the eye sees different colours, it actually perceives different wavelengths of light. When light directed towards an object any of the one of five things usually occurs depending on the emitted wavelengths and the composition of the object: Reflection:-whole of the light or a part of it can be reflected off the object making it appear white (if white light is emitted) or lighter (if only specific wavelengths are emitted). Absorption:- All or most of the light can be absorbed by the object. The object then appears black or darker. Reflection and Absorption:- A part of the light can be reflected, and part can be absorbed. It produces colours in the visible portion of the spectrum. Application of Video Spectral Comparator for Examination of Printed Material Page 17

3 Transmission:-Light can be transmitted through the object. Luminescence:- Light can strike the object, be absorbed, and then reemitted at a longer wavelength. The phenomenon is known as luminescence. Infrared (IR) and ultraviolet (UV) radiations are not visible to the human eye. However, all five mentioned effects that occur in the visible portion of the spectrum also occur in the IR and UV portions. There can be an important difference. The same object that absorbed light in the visible spectrum and appeared black, can now transmit radiant energy in the IR spectrum and appear clear like a piece of glass. For instance, the VSC5000 camera operating in the IR portion of the spectrum can capture an image lying underneath an opaque blue ink, similar to the way an X-ray captures images of bones through skin. Principle of VSC The VSC5000 consist of two components a desktop computer that runs on software and an imaging device that include7s a colour charge coupled device (CCD) video camera, a black and white CCD video camera, excitation/barrier filters, and various radiant energy sources (tungsten, halogen, and fluorescent lamps). The instrument is equipped with the specialized lighting tools for examination of documents. The visible, infrared, infrared luminescence, ultraviolet, transmitted, coaxial and the oblique lighting conditions may be used alone or in combination. The VSC5000 includes an automated spectrometer that uses the video camera and camera bandpass filter to analyze the light originating from some region of interest (ROI) in the document. VSC consist of a variety of illumination and filtering devices to reveal differences in IR absorption, transmittance, and luminescence and long wave UV excitation of visible luminescence (Fluorescence) of ink. By selecting different Illumination Modes, features hidden to the naked eye can be revealed. The instrument allows viewing and recording the response of documents/inks on exposure of light of various wavelengths. This is useful for the examination and comparison of inks, the examination of security features in documents such as passports and driving licenses, the examination of altered or obliterated entries and the examination of entries which have faded or Application of Video Spectral Comparator for Examination of Printed Material Page 18

4 been washed out. It permits the analysis and comparison of inks revealing alterations on a document. It visualizes security features printed into papers and allows a quick examination of the entire questioned document. Figure-2.1 The VSC-5000 Equipment The analysis may reveal ink differences in context, or similarities in chemical formulation. The graphical user interface allows examiners to control the VSC-5000 more easily. Spectral analysis is performed over the Wavelength band nm. comparisons can be made between images side by side on a split screen, overlaid or with strobe display with an image rotation feature for alignment.vsc facilitate colour measurement and chromaticity display charts and a high resolution grating spectrometer for recording absorption, reflectance, transmission and fluorescence spectra. Printing examination using Video Spectral Comparator The VSC-5000 can be used to examine printed documents. The examination under different lighting conditions can show that a document has been altered. If an additional paragraph or line has afterward been added to a document or a page is replaced with containing different information. Even without the source printer, it may be possible to opine that two documents were both produced using the same printer or not. Counterfeit pharmaceuticals, cigarettes, Application of Video Spectral Comparator for Examination of Printed Material Page 19

5 security documents etc can be examined by looking at the packaging. By comparison of with genuine packaging it is possible to link counterfeit packaging together by printing methods and defects. If the printers which have been used to produce the packaging are found then it is possible to link the counterfeits to the printers. Josey et al., (2000), reported comparisons of different models of the Foster & Freeman Video Spectral Comparator (VSC) equipment. The study discriminate matched pairs of black and blue liquid (water-based) and non-liquid writing inks by microscopy, VSC, Laser, and UV-IR-VIS spectroscopy. The VSC examinations were performed as monitor-assessed video spectral comparisons of IR, Infra Red Luminescence, and UV fluorescence responses of the inks. Liquid ink included roller-ball and fiber-tip; non-liquid included ballpoint. They concluded that VSC-1, successfully discriminated 79.50% of the pairs while the newer VSC-2000 correctly discriminated 95.80%. Of all the inks the older model did not discriminate, some were actually distinguishable by microscopic examination. 2.2 Experimental VSC Instrumentation The Windows based software version 5.7embedded in VSC 5000 from Foster + Freeman was utilized in the work. VSC-5000 provides the illumination by spot lamp, Flood light, UV-365, 312, 254, transmitted lights, coaxial light, anti-stokes and light from right & left side. In this study flood light was used which illuminate the sample from above. A flood light is an artificial light providing even illumination across a wide area. Table-2.1 The optical conditions of instrument used in study Process Lamp Type Spectrum Wavelength (nm) Illumination Incandescent Filament Lamp Filament Bulb Visible/IR Flood Application of Video Spectral Comparator for Examination of Printed Material Page 20

6 2.2.2 Scheme for Sample Collection The sample documents were collected in the form of printed documents from 32 inkjet printers. Each printout was containing four rectangular blocks of Cyan (aqua), Magenta, Yellow and Black colour. The colours were prepared by keeping the constant value of Red, Blue & Green in the colour palette of MS-Office (Nicholas 2003). Table 2.2 shows the values of Red, Green and Blue to create Cyan, Magenta, Yellow and Black colour. The RGB scheme used was as follows:- Table-2.2 Values of RGB (Red, Green, Blue) in colour palette of MS-Word application of Windows used for printing of documents on the same substrate of paper Bilt copier. Inkjet Ink R G B Cyan Magenta Yellow Black Paper used to print samples White paper of A4 size from Bilt Copier company manufactured in 2008 by Ballarpur Industries Limited GSM 75 was used throughout the study to take print sample Sample Preparation The list of printers used to print the sample documents are listed in Table 2.3 were collected from different markets of Hyderabad, New Delhi, Agra and Allahabad. During random sample collection majority of HP printers were encountered. Application of Video Spectral Comparator for Examination of Printed Material Page 21

7 Table-2.3 List of printers used to print the sample documents along with Brands & Models of Inkjet Printer S.No. Sample No. Model Brand- HP 1. 1 HP DeskJet 1050 J410 (M-1) 2. 2 HP DeskJet 1050 J410 (M-2) 3. 3 HP DeskJet 1050 J410 (M-3) 4. 4 HP DeskJet F HP PSC HP DeskJet D HP DeskJet HP Photosmart D HP DeskJet F HP Photosmart C HP DeskJet D1668 (M-1) HP DeskJet D1668 (M-2) HP Officejet HP DeskJet F HP Business Inkjet 1000 (M-1) HP Business Inkjet 1000 (M-2) HP Business Inkjet 1000 (M-3) Brand- Canon Canon Pixma MP Canon Pixma IP Canon Pixma MX Canon Pixma ip 1300 Brand- Epson Epson Stylus TX Epson R Epson Stylus Photo R230X Epson Stylus T13 (M-1) Epson Stylus T13 (M-2) Brand-Brother Brother MFC-295 CN Brother MFC-J415 W Brother DCP J125 (M-1) Brother DCP J125 (M-2) Brother DCP J125 (M-3) Brother DCP 6690 CW Application of Video Spectral Comparator for Examination of Printed Material Page 22

8 2.2.4 Sample Pool 32 coloured printouts were taken from different Inkjet printers. The Cyan, Magenta, Yellow and Black ink, the four major colour components were the target ink. The all coloured ink samples were then marked as the sample identification no. 1-C,2-C,3-C,4-C 32-C for Cyan colour ink, 1-M,2-M,3-M,4-M 32-M for Magenta colour Ink, 1-Y,2- Y,3-Y,4-Y 32-Y for Yellow Colour Ink and 1-K,2-K,3-K,4-K 32-K for Black colour Ink. 32 samples of each Cyan, Magenta, Yellow & Black Colour i.e. Total number of samples 32X4= 128 were analysed Analysis The sample to be examined was placed on the document platen under the canopy (Manual, VSC-5000). The document was viewed by a video camera and a live image was shown on the monitor. The document was then illuminated under flood light and the reflectance spectra were then recorded after selecting the position of the region of interest of the sample and standard white. A region of interest (ROI) was specified on the document from which the light is collected for analysis. The same procedure was then followed for recording spectra for all samples of four target inks. The images of sample document were documented by taking the images in normal flood light without any magnification Documentation The images of sample document were documented by taking the images in normal flood light without any magnification Consistency The reproducibility of the results for the same samples was checked 5 times by repeating the same experiments for five continuous days. Application of Video Spectral Comparator for Examination of Printed Material Page 23

9 2.3 Result and Discussion Usually document examiners are asked to examine printed documents and to fix their source of origin. Usually when the questioned document is a counterfeit currency, cheque, stamp papers etc or where, there is a small amount of document is present and where there court does not permit for the destructive examination then there is a need arrives for the technique which allows a non destructive examination of document. In order to overcome from this problem a spectral examination was conducted. The VSC5000 includes an automated Spectrometer that uses the Video Camera and Camera Bandpass Filter to analyze the light originating from some Region of Interest (ROI) in the document. Spectral analysis is performed over the Wavelength band nm (Manual VSC 5000, 2005).128 samples, 32 each for Cyan, Magenta, Yellow and Black were analyzed using VSC and the spectra were presented. Figure shows the graphs of all of the inks plotted as light intensity (expressed as a % of maximum) against wavelength over the range of 400 nm to 1000 nm. Figure 2.2 shows the comparative spectra of Yellow colour for HP brands. During the study it was found that Yellow colour inks are not easy to differentiate as all of the inks samples were showing the almost similar percentage of maximum intensity at same wavelength as shown in Figure Figure 2.3 shows the variation in sample no. 17 and 20 which are showing intensity at about 80% while the intensity of rest of the samples are almost equal around %. A little variation in sample no.25 is shown in Figure % % Figure 2.2: Comparative VSC spectra for Yellow colour of HP brands for sample number 1-4, Application of Video Spectral Comparator for Examination of Printed Material Page 24

10 90-100% Approx 80% Figure 2.3: Comparative VSC spectra for Yellow ink of sample no Figure 2.4: Comparative spectra of Yellow coloured ink for sample no , A little but significant variation was observed in the VSC spectra of Cyan and Magenta coloured ink as shown in Figure From the Figure 2.8 the distinct spectra of sample number 10 and 11 can be observed for various Magenta coloured ink samples. Application of Video Spectral Comparator for Examination of Printed Material Page 25

11 Figure 2.5: Comparative VSC spectra for Cyan ink for sample no.1-4,6-12. Figure 2.6: Spectra for Cyan colour for sample number Application of Video Spectral Comparator for Examination of Printed Material Page 26

12 Figure 2.7: Spectra of Cyan colour for sample number 23-29, Figure 2.8: Spectra for Magenta ink for sample no.1-4, Application of Video Spectral Comparator for Examination of Printed Material Page 27

13 Figure 2.9: The comparative spectra of Magenta coloured ink for sample no More significant variation was observed in the different sample of Black coloured ink. The ink samples of Black colour are showing absorbance at high wavelength, it may be due to the reason that the Black colour is a combination of several colours (Henry, 1917). As a trail TLC of black ink was carried out and it was found that black ink is a combination of several coloured inks. 100% 20% 20%-30% Figure 2.10: Comparative VSC spectra for Black coloured ink of all four brands sample no 1-4, 6, 8, Application of Video Spectral Comparator for Examination of Printed Material Page 28

14 90%-100% 25%-40% Figure 2.11: Comparative VSC spectra for Black colour of all four brands for sample number %-110% 20%-30% Figure 2.12: Comparative Spectra of Black colour for sample number 23-29, 31, 32. The variation in sample 2 in Figure 2.10 and in samples of Figure 2.11 and Figure 2.12 can be observed. Application of Video Spectral Comparator for Examination of Printed Material Page 29

15 2.4 Conclusion The VSC scan in the visible and partial NIR range ( nm) for various coloured inks (yellow, cyan, magenta) and black ink indicates characteristic absorption patterns. Among the same print colour inks of different manufacturer variations were observed which may be taken into account for forensic comparison. It was observed that the inter manufacturer difference were more in the magenta colour and maximum in black colour. In day to day document examination black printer inks are commonly encountered and hence the proposed methodology can be used successfully with confidence to differentiate between the black coloured cartridges of different manufacturers through their characteristic absorption spectra. The reasons for this are obvious as the black ink is a mixture of several colours and each manufacturer may be mixing different and specific colours in varying proportions. This variation can be used for the forensic comparison of the printed documents. In conclusion the proposed VSC technique can be used for the comparison of the printed documents. In conclusion the proposed VSC technique can be used for the comparison of various coloured print inks in general and more particularly the black inks. The technique is more suitable when the specimen comparison material is available. Application of Video Spectral Comparator for Examination of Printed Material Page 30