Dedication This book is dedicated to Sara Blitzer who provided support to me to fi nish my college education in physics and then start my professional career with the Eastman Kodak Company. She did this right after becoming widowed. Acknowledgments The authors wish to thank Lauren Marina Cregor, MA, for the initial proof- reading of the manuscript and providing a host of helpful suggestions. Also, to William Oliver, MD, for motivating this book by arguing the proposition that experts should be able to explain the basic processes associated with the image processing tools they use. Forward In American culture the fi eld of law and forensic science is often dramatized and over simplifi ed through television and media reports. Between “Law & Order” and “CSI” the public is exposed to scenarios of crime scene investi- gation and prosecution that are hyped on emotion and lacking in scientifi c foundation. The result is that the general public has a romanticized idea of what truly happens in the justice system and they have unrealistic expecta- tions of what science and the law is actually able to provide to a fi nder of fact in a legal setting. Forensic science is where law meets science in a forum where expert wit- nesses must be prepared to explain and defend their conclusions. Webster’s Dictionary defi nes “forensic” as: “belonging to, used in, or suitable to courts of judicature or to public discussion and debate.” The American Heritage College Dictionary defi nes “imaging” as: “to translate (photographs or other pictures) by computer into numbers that can be trans- mitted to and reconverted into pictures by another computer.” This book is intended to support initiatives that will allow individuals to be better edu- cated about the science of forensic imaging and the preparation necessary to offer testimony concerning forensic imaging in a legal context. It is impor- tant to fi rst remember the forum where the science meets the law, and then that the expert must be able to translate the scientifi c techniques and prin- ciples into a language and conclusion that a lay person will feel they can rely upon. Judges and juries are lay people for the most part and need to be prop- erly educated on what information can be relied upon and what cannot. A true expert is also prepared to explain the limitations of the science without apology or defensiveness so that the judge or jury can decide what weight and credibility should be given to the results. There are countless stories in the media of individuals who were con- victed and imprisoned and advances in forensic science later proved them to be innocent. Literally the results of scientifi c testimony can be a matter of life and death. However, juries have come to expect forensic science fi ndings will be presented at trials and may automatically judge the case weak if it is not. Forensic evidence is presented in a Court of law by having an individual qualifi ed as an expert describe the facts available, any quantitative or quali- tative measurements made, the application of the science to those facts and measurements, and the conclusions drawn stated as a matter of scientifi c certainty. This approach to presenting expert testimony is time honored and x Forward nothing new. But science is not a static fi eld of expertise, and as it progresses in technique and sophistication, the law and the witnesses presented to explain the science must adjust as well. There are many examples of cases that become battles of the experts. Evidence that might seem compelling and unimpeachable one day may be regarded as out-dated and unreliable the next. An example is fi ngerprint evidence which is often portrayed on televi- sion as almost as fi nite as DNA. However, the reality of gathering, preserv- ing and interpreting fi ngerprints is often a matter of controversy. This book reviews the fi eld of digital imaging and the science behind the more common tools and techniques is revealed. Anyone can snap a picture with a digital camera and produce an image rather easily using the available software. Being able to analyze that image and testify as to the content and whether the image is a “true and accurate depiction of what it is intended to portray” is a whole different responsibility. A number of complex tools must be used to analyze an image and testify that it has not been tampered with or the image distorted in a way that can skew the interpretation of the image. The expert must then be able to explain the basis for selecting the tools that were used, the order in which they were used and why the judge or jury should believe that these tools were the best and most appropriate to use in the analysis in question. Imagine that you are the member of a jury in a case involving allega- tions of domestic violence. The prosecutor introduces photographs through an expert that seem to depict serious injuries to the victim of the domestic abuse. The photographs show what appear to be redness, abrasions and pos- sible small lacerations to the victim’s face and the prosecutor argues that these are the result of a beating. The evidence seems most compelling. The defense then brings in an expert who testifi es that the photographs are, in fact, quite misleading. The defense expert attacks the camera used, the inap- propriate settings on the camera at the time the photographs were taken, how a combination of factors has caused exaggerations or artifacts in the images, and the fact that the victim suffers from a severe case of acne so that it is impossible to separate injuries from the skin condition given the photographic tools and techniques that were employed. What appeared to be compelling evidence may be interpreted as an effort on the part of the party offering the evidence to distort the truth. The case above is a simple example. But the use of forensic imaging is becoming more and more diverse. The areas in which imaging is being used include fi ngerprints, footwear and tire impressions, ballistics, tool marks, accident scenes, crime scene reconstruction, documentation of wounds or injuries, surveillance videos, and many others. Many of the cameras, scan- ners, software suites, printers and monitors or projectors are designed pri- marily for the consumer market or the artistic/commercial market. These tools are adequate when the intent is merely to evoke emotion or even create special effects. Knowledge of the science is not necessary or even considered. Forward xi But in forensic science the objective is quite different. The expert needs to be able to state a conclusion and feel confi dent in convincing the judge or jury that the conclusion is valid. To do this it is necessary to be able to know the major elements of the science behind the tools and explain what was done and why it was done that way. Forensics should be driven by truth seeking, not emotional impact. As with any fi eld of science, those now preparing to enter the fi eld of forensic science will need to be better prepared and educated than their pred- ecessors. They will also need to keep up with the ever accelerating pace of change. It is hoped this book will assist in supporting the new college cur- ricula and expanding degree programs in the fi eld of forensic science. Sonia J. Leerkamp, Prosecuting Attorney, Hamilton County, Indiana Introduction There are books that teach digital imaging technique and courses that teach one how to design cameras, computers, software, and other high-tech devices. The former are necessary to actually processing a case, but the con- tent is time sensitive because the specifi c devices and software packages change frequently. The latter are for engineers that will be designing devices and software for practitioners. This book is positioned between these two approaches. It discusses the science behind the devices and software and helps explain why commercially available items work the way they do and how to best use them to solve problems. It goes further in that it helps the forensic expert equip himself to answer tough questions that might arise regarding why he did what he did and why that is valid. The scientifi c basis is several decades old. Sharpening fi lters, unsharp mask techniques, brightness and contrast adjustment tools, and many other tools are derived from darkroom techniques that were developed, in some cases, over 100 years ago. The mechanism is now digital instead of analog, but the approach is the same. It is not likely that it will change dramati- cally in the near future; therefore, the material will have a certain degree of durability. There are some new digitally enabled tools that perform actions that are very diffi cult with analog photography, but the basis for these is not fundamentally new. For example the Fourier transform goes back to the early 1800s. It is just that modern computers make it an easy and fast tool to use. The fi rst four chapters: Why Take Pictures, Dynamic Range, Light and Lenses, and Photometry are quite general and are the foundation for much of what follows. The next chapter, Setting Exposures puts some of the basics together in ways that apply to photography. Then the chapter, Color Space brings up an old concept that needs to be made digital and is a cornerstone of digital photography and image processing. It is also a key in that it carries the means for the human visual system to utilize photographs.