VIDEO TAPE ENHANCEMENT
/ AUTHENTICATION - (Task Description)
| There are many situations where a surveillance
camera or the work of an amateur videographer has recorded important
information. Occasionally, because of deteriorating lighting, malfunctioning
equipment or poor technique, the recorded images are less than we
need in order to be useful as evidence. This is when Video Enhancement
through image processing can solve the problem.
Video Enhancement is a term that describes a number of different processes
used to correct for poor lighting or technique as well as some types of
camera or recording equipment failure. Never, in our application of Video
Enhancement, is the original recording damaged or altered in any way.
In most circumstances we will identify the significant degraded area and
then capture the best possible reproduction of that area into the computer
for enhancement purposes. Now begins the application of various techniques
to improve the captured image of the captured image. Some of these techniques
are quite complex, some are as simple as contrast and brightness adjustments.
When we start any enhancement task, it is absolutely imperative that we
start with the best possible image. This means the original recording.
We have all seen the photocopy of a photocopy of a photocopy... that is
barely readable. It is readable at all because we are using the most sophisticated
image processing system known (our eyes, visual cortex and brain) and
there are a limited number of valid shapes to interpret (upper and lower
case letters and numbers). When we are dealing with an image, we do not
have the advantage of interpreting only "a limited number of valid
shapes". We become much more sensitive to the degradation in the
image caused by even a first generation copy.
A first generation copy can put us so far behind the quality of the original
that we can waste a great deal of processing time just to get back to
the same level of clarity as the original. In addition, each copy looses
information and adds noise to the image. This lost information is data
that we can never have available to us for processing and in cases of
marginal images can easily make the difference in identification or elimination
of a suspect in a processed image.
Incidentally, it is important to realize that the original recording will
be degraded by continuous replay. Note the difference between your favorite
brand new video and the same one rented from your local video store. Replay
of an important section of video tape as few as 5 to 10 times can cause
obvious, permanent and unrecoverable loss of image quality.
Video Tape Authentication
Authentication of any type of recording is a verification that it is a
"Trustworthy" representation, in time, sequence and content,
of the event recorded. Even a simple press of the "pause button"
can be significant if it is determined that a period of time long enough
for the scene to be altered, in meaning or content, has elapsed.
Video Tape Authentication requires the examination of the original tape
and recorder that made that tape. We have extended the technique of using
magnetic development, documented in the Watergate examination, from audio
to video recording. The magnetic marks left by the recorder and frequently
not part of the visual image itself are examined to determine:
|| If the recording is the original or a copy
|| Which buttons were depressed
in the process of making that recording and where they are relative
to the video images being presented
|| If part of the original recording was masked
by recording over it at a later time
|| If the recorder presented is actually the
one used to make the tape being evaluated
|| Which of a limited number of recorders was
used to make a video recording
|| The answers to many other case specific
If the original recorder is not available, we still may be able to determine
if more than one recorder was used to make the video tape, but the ability
to specify that a particular recorder was involved is lost.
While authentication of a copy is not possible, if this is the best evidence
or simply all that is available, some of the information about the making
of the original recording can survive the copying process. This may be
enough information to allow us to suggest that certain recording events