1. Forensic Applications of Computer Vision
Peter Kovesi
Department of Computer Science
& Software Engineering
The University of Western Australia

2. Application areas Image enhancement Image metrology
Biometric identification

3. Video surveillance images are typically of poor quality
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.

4. 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.

5. Zooming in does not help!
Poor resolution:
Zooming in does not help!

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

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

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

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

10. Super-resolution from multiple
low resolution images:
Number plate reconstruction

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

12. Denoising
Grey scale enhanced image

13. original
deinterlaced
wavelet denoised and contrast enhanced

14. original
deinterlaced
wavelet denoised and contrast enhanced

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

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

19. 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.

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

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

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

24. Conclusion
Advances that have been made in Computer Vision, Photogrammetry and Projective Geometry over the last 10 years provide new opportunities for forensic science.