School of Electrical and Computer Engineering Inkjet Forensics Maria V. Ortiz Aravind K. Mikkilineni http://shay.ecn.purdue.edu/~prints 1 School of Electrical and Computer Engineering About the Presenters • Maria V. Ortiz – received her B.S. from the Universidad Javeriana, Bogota-Colombia in 2005. She is a Graduate Student at Purdue University where she holds a Research Assistantship on the department of Electrical and Computer. Schlumberger awarded her a scholarship as a recognition of her academic effort in 2004. Her thesis, based in the recognition of the Malaria, was nominated to “Best Engineering Thesis 2005” • Aravind K. Mikkilineni - received his B.S. in Electrical and Computer Engineering from Ohio State University in Columbus, Ohio in 2002. In 2004 he received his M.S. in Electrical and Computer Engineering from Purdue University while working as a research assistant in the area of printer security and forensics. He is currently working toward a Ph.D. at Purdue University while continuing work on printer and device forensics. September 27, 2006 ENFSI-EDEWG 2 2 School of Electrical and Computer Engineering Electronic Imaging Systems Laboratory • Prof. Jan P. Allebach • Investigate imaging systems (printers, scanners, digital cameras and displays) • Characterize imaging systems – Perform measurements and analysis on imaging systems – Identify problematic sources in black box models • Improve imaging systems – Test solutions on systems – Test solutions on human participants (psychophysics experiments) – Improve solutions model to integrate the human perception – Implement solution model September 27, 2006 ENFSI-EDEWG 3 3 School of Electrical and Computer Engineering VIPER Lab • Video and Image Processing • Prof. Edward J. Delp • Video Coding • Device Forensics • Watermarking • Document Security • Sensor Networks September 27, 2006 ENFSI-EDEWG 4 4 School of Electrical and Computer Engineering Agenda • Introduction to digital printing • Basic inkjet printing process • Digital Imaging • Inkjet details • Short Lab – (Identifying print process parameters) • Print modes (print driver settings) • Examination of Print Samples [#] indicates a reference which are listed at the end of the presentation September 27, 2006 ENFSI-EDEWG 5 5 School of Electrical and Computer Engineering Basic Inkjet Printing Process • Paper path • Carriage • Cartridge • Print head • Inkjet printing technologies September 27, 2006 ENFSI-EDEWG 6 The paper path along with the carriage, the cartridge, and the printhead are involved in every inkjet printing process and their interaction depends on the printing technology of the printer. 6 School of Electrical and Computer Engineering Overview of the Inkjet Process September 27, 2006 ENFSI-EDEWG 7 7 School of Electrical and Computer Engineering Paper path Paper is advanced through the printer A carriage transports the pen back and by a series of rollers driven by a forth across the page. The pen fires ink [3] stepper motor. onto the surface of the page. September 27, 2006 ENFSI-EDEWG 8 Red arrows show the printing direction Blue arrow shows the process direction 8 School of Electrical and Computer Engineering Carriage September 27, 2006 ENFSI-EDEWG 9 These pictures were taken from the printer model we used in the demo session The region highlighted in red is an optical encoder strip which is used by the printer to position the carriage for proper dot placement. The image on the right shows the carriage which carries the printhead and the cartridge/cartridges. This printer uses two cartridges, one for color and the other for black. 9 School of Electrical and Computer Engineering Cartridge [2][9][21] September 27, 2006 ENFSI-EDEWG 10 Different types of cartridges. The cartridges on the right do not carry the printhead. Instead, in this kind of printer, the printhead is fixed to the carriage in the printer. The middle cartridges have the printhead attached to them and as a consequence the printhead is replaced with the cartridge. On the left, we can see the electrical contacts between the cartridge and the printer. 10 School of Electrical and Computer Engineering Printhead/Nozzles 1/600 in 1/300 in 1/600 in September 27, 2006 ENFSI-EDEWG 11 The printhead is composed of nozzles which eject drops of ink out of the cartridge and onto the paper. This diagram illustrates the nozzle placement for a printer with a resolution of 600dpi . Since the separation between them is very small, the nozzles are arranged in multiple offset columns (in this case two) because of mechanical limitations and to help avoid coalescence where two adjacent drops will merge into one drop. 11 School of Electrical and Computer Engineering Inkjet Printing Technologies [1] September 27, 2006 ENFSI-EDEWG 12 Inkjet printing is divided into continuous and drop-on-demand technologies. In the continuous inkjet technology the drops are formed continuously but only some of them are expelled, on the other hand, in the drop-on-demand inkjet technology the drops are generated as needed. 12 School of Electrical and Computer Engineering Thermal Inkjet Side-shooter Roof-shooter [1] September 27, 2006 ENFSI-EDEWG 13 The thermal inkjet technology is divided in two categories according to the position of the heater element, side shooter and roof shooter. As the temperature increases, the heater and the ink get hotter, until a bubble is formed and by the pressure in the ink reservoir, a drop is fired out the cartridge. 13 School of Electrical and Computer Engineering Piezoelectric Inkjet Bend mode Classification depends on the piezoceramic deformation mode. Four main types: • Squeeze-mode can be designed with a thin tube of piezoceramic surrounding a glass nozzle or with a Push mode piezoceramic tube cast in plastic that encloses the ink channel. • Bend-mode design, the piezoceramic plates are bonded to the diaphragm forming an array of bilaminar electromechanical transducers used to eject the ink droplets. • Push-mode design, as the piezoceramic rods expand, Shear mode they push against ink to eject the droplets. • Shear-mode the electric field is designed to be perpendicular to the polarization of the piezodriver. The shear action deforms the piezoplates against ink to eject the droplets. [1] September 27, 2006 ENFSI-EDEWG 14 On the piezoelectric printers, the deformation of a piezoceramic material reduces the space inside the ink chamber and a drop is expelled. There are four categories depending on the piezoceramic element used. 14 School of Electrical and Computer Engineering Digital Imaging Image formation and associated artifacts September 27, 2006 ENFSI-EDEWG 15 Understanding digital imaging artifacts and being able to distinguish them from printer artifacts is essential. 15 School of Electrical and Computer Engineering Digital versus Printer Artifacts Stepping: the imperfection of drawing of long lines sloped at a very small angle. [13] [19] September 27, 2006 ENFSI-EDEWG 16 Stepping, the jaggedness seen on edges of straight or curved lines, is a digital artifact that could be mistaken for a printer artifact. 16 School of Electrical and Computer Engineering Halftoning September 27, 2006 ENFSI-EDEWG 17 Understanding textures created by the process of halftoning are also important to understand. Small dots visible in light halftoned regions should not be mistaken for stray printer dots. 17 School of Electrical and Computer Engineering Inkjet Details • Performance vs. image quality • Ink drop formation and ejection • Dot structure • Swath alignment and Passes • Multi-pass, single-pass, and print masks • Page edge artifacts • Paper interaction • Ink types September 27, 2006 ENFSI-EDEWG 18 18 School of Electrical and Computer Engineering Performance Versus Image Quality Hardware Logic Printhead Velocity Pen size and Firing Frequency Print Mechanism Output Resolution Ink/Media Ink Ability to Mask Defects [21] Capacity Ink Flux September 27, 2006 ENFSI-EDEWG 19 Every process involved in creating an inkjet print is important and cause an inherent tradeoff between printing speed/performance and print quality. 19 School of Electrical and Computer Engineering Drop Ejection [14] September 27, 2006 ENFSI-EDEWG 20 The drops are ejected out of the cartridge though the nozzles. As the drop falls from the cartridge to the media, it splits into the main body or primary drop and the secondary drop. The secondary drop should fall on top of the primary one but some aerodynamic effects prevent such event to happen. Notice that some of the ink is soaked up again by the empty space that was left in the ink reservoir. 20 School of Electrical and Computer Engineering Dot Structure Satellite Tail [3][4] September 27, 2006 ENFSI-EDEWG 21 When the secondary drop does not fall on the same spot as the primary drop, it becomes either a satellite of a tail. Satellite : secondary dot is not attached to the main dot Tail : secondary dot is attached to the primary dot Using the position of the satellites or tails you can find out the printing direction Left to right: satellite/tail on the right side of the main dot Right to left: satellite/tail on the left side of the main dot leading the printing direction. 21 School of Electrical and Computer Engineering Effect of Carriage Speed on Dot Structure 15 ips left to right 45 ips left to right 45 ips right to left [3] September 27, 2006 ENFSI-EDEWG 22 A slow print speed causes satellite drops to fall on top of or near the main drop as seen in the left image. As the print speed increases, the satellite drop falls further from the main drop as seen in the right two images. 22 School of Electrical and Computer Engineering Dot Placement Error Horizontal dot displacements Horizontal dot displacements for even raster for odd raster Vertical dot displacements for even raster Vertical dot displacements for odd raster [4] September 27, 2006 ENFSI-EDEWG 23 Due to the position of the nozzles on the printhead (i.e. the space between the two columns) there is a misplacement of the dots in the horizontal position while in the vertical position there is not such error.