Forensic Applications of Video and Digital Photography

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Forensic Applications of Video and Digital
Photography
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What is a Digital Camera?
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Digital Imaging Evolution
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How Digital Cameras Work

• Digital Cameras have a sensor that converts light
  into electrical charges.
• The image sensor employed by most digital cameras
  is a charge coupled device (CCD).
• Some low-end cameras use complementary metal
  oxide semiconductor (CMOS) technology.
• While CMOS sensors will almost certainly improve
  and become more popular in the future, they
  probably won't replace CCD sensors in higher-end
  digital cameras.

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How Digital Cameras Work

• The CCD is a collection of tiny light-sensitive
  diodes, which convert photons (light) into
  electrons (electrical charge).
• These diodes are called photosites. In a
  nutshell, each photosite is sensitive to light --
  the brighter the light that hits a single
  photosite, the greater the electrical charge that
  will accumulate at that site.

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Several Types of Digital Cameras

• Floppy Disk
• 3 inch CD-R
• Memory Stick
• Compact Flash Card
• SmartMedia Cards
• Built-in Memory

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Image Acquisition

• Solid-state arrays are composed of discrete
  silicon imaging elements (photosites) providing
  voltage output
• Line scan sensors (resolution 256 to 4096)
• Area sensors (32 x 32, 256 x 256, 640 x 480,
  1280 x 1024)
• with CCD chip 2048 x 2048

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Resolution

• Pixel
• A digital image is made up of hundreds of
  thousands of tiny dots
• Resolution
• Number of horizontal pixels multiplied by the
  number of vertical pixels
• More Pixels the sharper the image

• Cropping photos allows one to make high
  resolution photos small enough to print and keep
  a lot of detail
• 640 X 480 web, email
• 1024 X 768 3 X 5
• 1280 X 960 5 X 7
• 1600 X 1200 8 X 10
• Or extra-sharp 5 X 7
• 1920 X 1600 Very High Resolution

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How to Compare Digital Cameras

• The higher the amount of megapixels the better
  the resolution
• For long range photography you will want a
  digital zoom
• Small vs. Big- The Sony Mavica FD97s shoot a
  great picture but are very bulky and heavy
• What machine will you be downloading to? Windows
  95 machines without an adaptor will not accept
  memory cards.
• Convenience memory cards, speed of downloads

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How to Compare Digital Cameras

• Glass lens vs.plastic lens
• If you will only output pictures to a computer
  monitor (for viewing, Web page use or email) an
  inexpensive digital camera with a 640X480 pixel
  resolution will provide satisfactory results
• If you plan to print photographs on a good (at
  least 720 dots per inch) color printer, look for
  a high resolution camera

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Choosing a Camera

• Digital Zoom
• Magnifies the image using the pixels in the
  image.
• Does not telescope into a subject
• It Interpolates the picture magnifying the
  existing pixels
• Best used in high resolution pictures
• Leads to fuzzier, less defined image

• Optical Zoom
• Magnifies the image using a real
  multifocal-length lens
• 2X, 3X, .14X
• Means that if the cameras minimum focal length
  is 50mm, then it has the ability to take pictures
  up to 100mm
• Or 2X as far as the image in a fixed lens.

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Digital Camera Features

• Exposure Compensation
• Allows for minor adjustments to the automatic
  exposure settings, allowing one to lighten or
  darken scenes with difficult lighting situations,
  such as backlit or high contrast scenes

• White Balance
• Allows one to set the white point for the
  picture. Setting a manual white point will
  allow one to adjust ones pictures colors to get
  what the actual color is really.

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Photo Compensation
If you wish to make the result whitish, operate
the exposure compensation button (or dial) to
(plus) side (at 2 EV, the entire frame becomes
almost pure white).On the other hand, if you
wish to make it blackish, adjust it to - (minus)
side (at -2 EV, the entire frame becomes almost
pure black).
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White Balance
Example of a shot taken under the light of a
tungsten bulb with "Fine ("SUNNY")" white
balance setting.
Example of a shot under the lighting of a
fluorescent lamp with "AUTO" white balance setting
Example of a shot taken under the sun with
"Incandescent" white balance setting.
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Tips on Taking Photos

• Avoid the dreaded blur
• Stand Still
• Hold the camera steady and firmly with both hands
• Use the viewfinder instead of the LCD monitor

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Tips Continued

• Eye level with subject
• Flash
• Stay within the effective range of the cameras
  flash
• 3 to 10 feet
• Move to close and get overexposure
• To far away and underexposure

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Tips Continued

• Outdoor Flash
• Makes photos more vibrant with more punch,
  separating the subject from the background
• Yielding sharper photo
• Especially in low light

• Be Prepared
• Carry extra batteries
• Memory Cards or Disk
• TIFF and JPEG
• TIFF longer to record but much higher quality

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Storage

• Short-term for use during processing
• computer memory
• frame buffers (up to 32 Mbytes of storage)
• On-line for fast recall
• Magnetic discs, optical discs
• Archival storage (infrequent access)
• Magnetic tapes (short shelf life)
• WORM optical discs

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Image Storage
Image is converted to data and stored on cameras
memory card.
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Two Factors That Affect Image Quality
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Two Factors That Affect Image Quality
File Compression

Image Resolution
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File Compression

• Compressing an image reduces the amount of memory
  that is taken up by the image but

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File Compression

• compressing an image also reduces the quality of
  the image.

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Image Resolution - Whats a pixel?
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Image enlarged 800x
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Pixel
12 x 12 144

• A pixel is the smallest piece of information that
  a digital image is made from.

Resolution 144
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Pixel

• The greater the number of pixels, the higher the
  resolution of the image.

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Original Image360 x 28050 KBytes
Resolution reduced to 150 high x 120wide 18
KBytes
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Image enlarged from 150 wide x 120 high back to
the original size of 360 wide x 280 high.
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Image types
.jpg
.gif
.bmp
Graphics Interchange Format Use when graphic has
only a few colours Drawings clipart maps
(or jpeg) Joint Photographics Experts Group Use
when image has lots of colours e.g. photograph
Bitmaps Made up of dots. Value of dots are stored
in bits of data
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Digital Camera Formats

• Still images are recorded in JPEG formatJPEG
  (pronounced "jay-peg") is a standardized image
  compression mechanism.
• JPEG stands for Joint Photographic Experts Group,
  the original name of the committee that wrote the
  standard.
• JPEG is designed for compressing either
  full-color or gray-scale images of natural,
  real-world scenes. It works well on photographs,
  naturalistic artwork, and similar material not
  so well on lettering, simple cartoons, or line
  drawings. JPEG handles only still images, but
  there is a related standard called MPEG for
  motion pictures.
• If one makes changes each time to a JPEG the
  resolution is compromised over time

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Digital Camera Formats

• Clip Motion images are stores in GIF Format
• GIF stands for "Graphic Image Format", and the
  format was developed by Compuserve to provide a
  means of passing an image from one dial-up
  customer to another, even across different
  computer hardware platforms.
• It is a relatively old format, and was designed
  to handle a palette of 256 colors (8 bit color),
  and a single image. When developed, this was near
  state of the art for most personal computers.

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Digital Camera Formats

• Movies are shot in MPG M-PEG
• 1. Abbreviation for Motion Picture Experts Group.
  2. In digital television signal recording or
  transmission, the designator that identifies a
  certain coding algorithm having several levels
  and profiles, the most sophisticated of which are
  used for HDTV (high-definition television)
  applications.
• 3.Pertaining to files (with file-name extensions
  ".mpg" or ".mpeg") that are compressed using the
  MPEG standard.
• Also written MPEG.

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Transferring Images to the Computer
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• Application areas
• Image enhancement
• Image measurement
• Biometric identification

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Image Enhancement
Video surveillance images are typically of poor
quality
camera
video recorder
monitor
The quality of the display on the monitor can be
misleading. The video recorder runs 24
hours/day. ? The tape gets worn and the recording
heads get dirty. ? The images that are recorded
can be very poor.
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Image Enhancement

• Common problems in images
• Poor resolution, especially in video images.
• Poor contrast due to under or over-exposure.
• Corruption with noise.
• Motion blur or poor focus.
• Misalignment of rows from line jitter and
  interlacing of motion in video images.

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Poor resolution Zooming in does not help!
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Create a higher resolution image by
mathematically interpolating pixel values
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Super-resolution from multiple low resolution
images
Images must be aligned accurately. Object should
be planar.
Irani and Peleg 1991 Capel and Zisserman 1998
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Super-resolution from multiple low resolution
images
Results from synthetic data can be impressive
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Real data Car number plate - low resolution
blur and noise.
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Super-resolution from multiple low resolution
images
Number plate reconstruction
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Denoising
Current method of choice is wavelet shrinkage
denoising.
Donoho and Johnson 1995
original image
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Denoising
Grey scale enhanced image
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original
deinterlaced
wavelet denoised and contrast enhanced
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original
deinterlaced
wavelet denoised and contrast enhanced
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Image Metrology
Calibration targets allow views of flat surfaces
to be rectified. Rectified views allow
measurements to be taken.
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Image Metrology
Rectified views of the fence and ground.
Criminisi, Reid and Zisserman 1999
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If a 3D calibration frame is placed in a scene
and photographed from two or more directions 3D
measurements can be made.
Image Metrology
However, care is needed to get accurate results.
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Image Metrology
Stereo reconstruction
3D Measurements can be taken from the photographs
long after the scene has been destroyed.
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Image Metrology
Some measurements can be made in an uncalibrated
image if you can determine vanishing points and
the horizon.
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An unknown height can be determined if you know
the horizon, the vertical vanishing point and a
reference height.
Criminisi, Reid and Zisserman 1999
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• Video Surveillance Applications
• Transport Applications
• Airports, Border, Railways, Underground, and
  Roadway
• Public Places
• Banks, Supermarkets, Homes, Department Stores,
  Parking Lots
• Law Enforcement and Military
• Forensic Applications, Remote Surveillance
• Trend Distributed Video Surveillance Networks

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Video Surveillance is Everywhere
Transport Applications Airports, Border,
Railways, Underground, and Roadway Public
Places Banks, Supermarkets, Homes, Department
Stores, Parking Lots Law Enforcement and
Military Forensic Applications, Remote
Surveillance
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First Generation

• Analog CCTV Cameras Analog Video Tapes
  Recording
• Complete Human Monitoring

Multiplexer
Analog Monitor
Video Recorder
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Second Generation

• Analog CCTV Cameras Digital Video Recording
• Automatic Event Detection based on Motion
  Detection

Alarm I/O
Monitor
Multiplexor
TCP/IP Network
DVR
(Image Source Axis)
Cameras
(Image Source Mobotix)
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Third Generation

• Complete Digital Solutions IP Cameras Network
  Video Recording
• Multi-Camera Cooperated Object Detection,
  Tracking, and Event Analysis

(Image Source MIT CSAIL)
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DVSN Next Step of Video Surveillance?
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To succeed, a new approach to video surveillance
is required
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Acknowledgements Slides have been used from a
presentation by Peter Kovesi Department of
Computer Science Software Engineering The
University of Western Australia