biometrics & security tutorial 7. 1 (a) please compare two different kinds of biometrics...
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Biometrics & Security
Tutorial 7
• 1 (a) Please compare two different kinds of biometrics technologies: Retina and Iris. (P8:2-3)
• 1 (b) Understand the retina recognition system. Please give the differences between retinal identification and retinal authentication. (P8: 10-11)
• 1 (c)P8:20 show a representative example of identification system. Please give another example of verification system.
• 1 (d) Please understand the iris recognition system. (P8: 22-36)
• 1 (e) What is texture feature (P8: 30)? Why we can use texture feature in iris recognition (P8: 31)?
• 2. There are four steps in the Daugman’s approach (P8: 32-36). The third step generates IrisCode with 512 bytes. If 2 bits represent a feature, please compute the total number of features. (512*(8/2)=2,048)
• Hamming distance: the distance between two vectors A and B is ∑ | Ai - Bi |.
General idea of Iris Code
• 3. In P8:37, an example of iris verification distributions is given. Notice that Hamming distance is defined to measure the similarity of two IrisCodes.
• Which value in the figure can separate two parts, authentics and imposters?
• If the similarity between two IrisCodes is taken as 0.5, can you say they are identical?
• How about the comparison result when the similarity is 0.2?
• What conclusion will you get from the hamming distance used to compute similarity of IrisCodes? (0.38; no; yes)
True Acceptance Rate
• A genuine individual is accepted. (TAR)
T hre shold (M a tc h ing sc ore s)
T A R
0
1
Total True AcceptanceTAR
Total True Attempts
Threshold=0 means that the attempts whose matching score >0 will be accepted; (everybody will be accepted)
Threshold=∞ means that the attempts whose matching score > ∞ will be accepted (nobody will be accepted)
False Rejection Rate
• A genuine individual is rejected. (FRR)
Total False RejectionFRR
Total True Attempts
T hre shold (M a tc h ing sc ore s)
F R R
0
1
Threshold=0 means that the attempts whose matching score <0 will be rejected;(nobody will be rejected)
Threshold=∞ means that the attempts whose matching score < ∞ will be rejected(everybody will be rejected)
True Rejection Rate
• A impostor is rejected. (TRR)
Total True RejectionTRR
Total False Attempts
T hre shold (M a tc h ing sc ore s)
T R R
0
1
Threshold=0 means that the attempts whose matching score <0 will be rejected;(nobody will be rejected)
Threshold=∞ means that the attempts whose matching score < ∞ will be rejected(everybody will be rejected)
False Acceptance Rate
• A impostor is accepted. (FAR)
Total False AcceptanceFAR
Total False Attempts
T hre shold (M a tc h ing sc ore s)
F A R
0
1
Threshold=0 means that the attempts whose matching score >0 will be accepted; (everybody will be accepted)
Threshold=∞ means that the attempts whose matching score > ∞ will be accepted (nobody will be accepted)
ROC
• There are some trade off among TAR, FRR, TRR, FAR.
• We need a particular threshold to keep the TAR and TRR as high as possible and to keep FAR and FRR as low as possible.
• We need the ROC curve to find the optimal threshold.
• We also use ROC curve to evaluate the system
ROC(2)
T A R
0
1
1
R O C C urve
F A R
F A R
0
1
1
R O C C urve
F R R
Find the optimal point (threshold)
• 4. P8:27 shows the corresponding Fourier transforms of iris images with different quality. Please give the property of Fourier transform of good quality iris images. (Even distribution)
Fourier Transform
• Any signal can be expressed as a weighted sum of a series of sine or cosine wave
• a is the original signal• a = w1∙b + w2∙b + w3∙d• b is a low frequency component• d is a high frequency component
=
3 sin(x) A
+ 1 sin(3x) B A+B
+ 0.8 sin(5x) CA+B+C
+ 0.4 sin(7x) DA+B+C+D
A sum of sines and cosines
sin(x) A
• 5. In Daugman’s approach iris is regarded as a circular pattern (P8: 32-36). In fact we can also take the iris as other pattern, as shown in P8: 29. Please try to design the corresponding scheme.