Marcus Borengasser, Ph.D.
Forensic image processing (FIP) involves the computer restoration and enhancement of surveillance imagery.
The goal of FIP is to maximize information extraction from surveillance imagery, especially imagery that is
noisy, incomplete, or over/under exposed. Although this definition is with respect to surveillance imagery,
FIP techniques can be applied to other types of images, such as retinal images, shoe impression images, UAV
(unmanned aerial vehicle) infrared images, and more.
Often, for a variety of reasons, the quality of surveillance imagery is very low. The low imagery quality
can be caused by poor lighting, poor media quality (analog systems), excessive motion of the subject, a
camera in need of calibration, and noise introduced by the imaging/recording system. With digital filtering,
image restoration, de-noising, and enhancement techniques, information can often be extracted from low
Forensic imaging processing is a method of improving a digital image (surveillance, closed circuit TV,
infrared, etc.) using a variety of computer techniques. These techniques often involve digital “filters” that
can suppress noise in the digital image, aid in the extraction of detail from shadow, and provide image
sharpening. As will be discussed in a later article, the distribution of image pixels (histogram) can also be optimized for
Definition and Enhancement of a Digital Image
An image can be considered as a two-dimensional function,
f(x,y), where x and y are plane coordinates such as latitude/
longitude in the case of a UAV image, and the value of f at
any location (x,y) is the intensity or gray level of the image
at that point. The intensity or gray level is directly related to
the brightness of the subject that was imaged. Forensic image processing techniques can then be consid-
ered to be a transformation that is applied to an input image to produce an output image, such as:
g(x,y) = T [f(x,y)]
Although digital images can be enhanced by forensic image processing techniques, image editing
techniques, such as variations in exposure conditions, cropping, dodging/burning, are not considered to
be forensic image processing. In general, FIP (or just image processing) techniques involve changing pixel
values in one way or another, while image editing techniques typically do not change pixel values.
Forensic Image Processing as a Profession
FIP is important to a variety of professions, such as criminologist, law enforcement, Homeland Security,
private security, military, U.S. Postal Service, the Secret Service, etc. In general, these professionals use
FIP for analysis of crime scene surveillance data. The crimes can be anything from bank robbery to arson
to breaking/entering to a terrorist attack. Businesses and corporations can also use surveillance systems and
the subsequent imagery to ensure that employee behavior is consistent with company policy.
Forensic imaging processing is
a method of improving a digital
image using a variety of com-