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Forensic Applications of Video and Digital Photography.

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Presentation on theme: "Forensic Applications of Video and Digital Photography."— Presentation transcript:

1

2 Forensic Applications of Video and Digital Photography

3 What is a Digital Camera?

4 Digital Imaging Evolution Digital Cameras Scanners Film Cameras Computer Cell Phones Devices CD/Floppy Home Printing Retailers Internet email

5 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.

6 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.

7 Several Types of Digital Cameras Floppy Disk 3 inch CD-R Memory Stick Compact Flash Card SmartMedia Cards Built-in Memory

8 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

9 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

10 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

11 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

12 Choosing a Camera Optical Zoom –Magnifies the image using a real multifocal-length lens 2X, 3X, ….14X Means that if the camera’s 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. 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

13 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 one’s picture’s colors to get what the actual color is really.

14 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).

15 White Balance Example of a shot under the lighting of a fluorescent lamp with "AUTO" white balance setting Example of a shot taken under the light of a tungsten bulb with "Fine (="SUNNY")" white balance setting. Example of a shot taken under the sun with "Incandescent" white balance setting.

16 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

17 Tips Continued Eye level with subject Flash –Stay within the effective range of the camera’s flash 3 to 10 feet Move to close and get overexposure To far away and underexposure

18 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

19 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

20 Image is converted to data and stored on cameras memory card. Image Storage

21 Two Factors That Affect Image Quality

22 File Compression Image Resolution & Two Factors That Affect Image Quality

23 File Compression Compressing an image reduces the amount of memory that is taken up by the image but…

24 File Compression …compressing an image also reduces the quality of the image.

25 Image Resolution - What’s a pixel?

26 Image enlarged 800x

27 Pixel A pixel is the smallest piece of information that a digital image is made from. 12 x 12 = 144 Resolution = 144

28 The greater the number of pixels, the higher the resolution of the image. Pixel

29 Original Image 360 x 280 50 KBytes Resolution reduced to 150 high x 120wide 18 KBytes

30 Image enlarged from 150 wide x 120 high back to the original size of 360 wide x 280 high.

31 Image types.gif.jpg 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.bmp Bitmaps Made up of dots. Value of dots are stored in bits of data

32 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

33 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.

34 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.

35 Transferring Images to the Computer

36 Application areas Image enhancement Image measurement Biometric identification

37 Video surveillance images are typically of poor quality cameravideo 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. Image Enhancement

38 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.

39 Poor resolution: Zooming in does not help!

40 Create a `higher resolution’ image by mathematically interpolating pixel values

41 Super-resolution from multiple low resolution images Images must be aligned accurately. Object should be planar. Irani and Peleg 1991 Capel and Zisserman 1998

42 Results from synthetic data can be impressive Super-resolution from multiple low resolution images:

43 Real data: Car number plate - low resolution + blur and noise.

44 Super-resolution from multiple low resolution images: Number plate reconstruction

45 Denoising original image Current method of choice is wavelet shrinkage denoising. Donoho and Johnson 1995

46 Denoising Grey scale enhanced image

47 originaldeinterlaced wavelet denoised and contrast enhanced

48 originaldeinterlaced wavelet denoised and contrast enhanced

49 Image Metrology Calibration targets allow views of flat surfaces to be rectified. Rectified views allow measurements to be taken.

50 Image Metrology Rectified views of the fence and ground. Criminisi, Reid and Zisserman 1999

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53 Image Metrology If a 3D calibration frame is placed in a scene and photographed from two or more directions 3D measurements can be made. However, care is needed to get accurate results.

54 Image Metrology Stereo reconstruction 3D Measurements can be taken from the photographs long after the scene has been destroyed.

55 Image Metrology Some measurements can be made in an uncalibrated image if you can determine vanishing points and the horizon.

56 Criminisi, Reid and Zisserman 1999 An unknown height can be determined if you know the horizon, the vertical vanishing point and a reference height.

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58 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

59 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

60 First Generation Analog CCTV Cameras + Analog Video Tapes Recording Complete Human Monitoring MultiplexerAnalog MonitorVideo Recorder

61 Second Generation Analog CCTV Cameras + Digital Video Recording Automatic Event Detection based on Motion Detection TCP/IP Network Multiplexor Alarm I/O Monitor Cameras DVR (Image Source: Axis) (Image Source: Mobotix)

62 Third Generation Complete Digital Solutions: IP Cameras + Network Video Recording Multi-Camera Cooperated Object Detection, Tracking, and Event Analysis (Image Source: MIT CSAIL)

63 DVSN: Next Step of Video Surveillance?

64 Camera, Sensors and Video Equipment Transfer Management Storage Integration Support Analytics To succeed, a new approach to video surveillance is required

65 Acknowledgements Slides have been used from a presentation by Peter Kovesi Department of Computer Science & Software Engineering The University of Western Australia


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