For both the averaging technique and removal technique undistorted duplicates of the original images were processed for recognition in order to determine a best-case rate for recognition. For both techniques and for all three data sets, rates of recognition stabilized as the number of eigenfaces used in the recognition scheme increased.
For each image set stability was reached at the following hit rate and for the specified number of eigenfaces:
Table 1. Number of Eigenfaces for Hit Rate Stability for All Image Sets
| Image Set |
Stable Hit Rate |
Number of Eigenfaces |
| Rice (Average) |
90% |
11 |
| AT&T (Average) |
86% |
17 |
| Yale (Average) |
68% |
21 |
| Rice (Removal) |
67% |
14 |
| AT&T (Removal) |
96% |
12 |
| Yale (Removal) |
75% |
20 |
For detection tests using a number of eigenfaces greater than that specified in Table 1 no significant improvement in detection success rate was achieved. In this way, undistorted tests suggest that implementations for both averaging and removal techniques do not achieve greater detection rates with numbers of eigenfaces greater than the minimum number needed for stability.
For both averaging and removal techniques Rice image sets were tested for detection rates with horizontal and vertical occlusions centered on the vertical and horizontal axes respectively. Results show that hit rate stability, as before, is achieved as the number of eigenfaces used increases.
For each image set stability was reached at the following hit rate and for the specified number of eigenfaces:
Table 2. Number of Eigenfaces for Hit Rate Stability for Rice Image Set, Averaging Technique
| Occlusion |
Stable Hit Rate |
Number of Eigenfaces |
| Horizontal 1 pixel |
90% |
13 |
| Horizontal 10 pixels |
72% |
7 |
| Horizontal 40 pixels |
28% |
4 |
| Vertical 1 pixel |
90% |
11 |
| Vertical 10 pixels |
83% |
7 |
| Vertical 40 pixels |
71% |
5 |
Table 3. Number of Eigenfaces for Hit Rate Stability for Rice Image Set, Removal Technique
| Occlusion |
Stable Hit Rate |
Number of Eigenfaces |
| Horizontal 1 pixel |
72% |
11 |
| Horizontal 10 pixels |
72% |
12 |
| Horizontal 40 pixels |
56% |
14 |
| Vertical 1 pixel |
72% |
11 |
| Vertical 10 pixels |
74% |
12 |
| Vertical 40 pixels |
72% |
15 |
For detection tests using a number of eigenfaces greater than that specified in Tables 2 and 3 no significant improvement in detection success rate was achieved. In this way, occlusion tests suggest that implementations for both averaging and removal techniques do not achieve greater detection rates with numbers of eigenfaces greater than the minimum number needed for stability without occlusions.
For both averaging and removal techniques, Rice image sets were tested for detection rates after being filtered with a two dimensional boxcar blur of various lengths. Results continue to indicate that the use of eigenfaces beyond the minimum necessary to achieve stability in the undistorted case is still unnecessary.
For each image set stability was reached at the following hit rate and for the specified number of eigenfaces:
Table 4. Number of Eigenfaces for Hit Rate Stability for Rice Image Set, Averaging Technique
| Boxcar Length |
Stable Hit Rate |
Number of Eigenfaces |
| 2 pixels |
90% |
12 |
| 20 pixels |
80% |
13 |
| 40 pixels |
67% |
15 |
Table 5. Number of Eigenfaces for Hit Rate Stability for Rice Image Set, Averaging Technique
| Boxcar Length |
Stable Hit Rate |
Number of Eigenfaces |
| 2 pixels |
72% |
9 |
| 20 pixels |
66% |
14 |
| 40 pixels |
44% |
15 |
For detection tests using a number of eigenfaces greater than that specified in Tables 4 and 5 no significant improvement in detection success rate was achieved. In this way, blurring tests suggest that implementations for both averaging and removal techniques do not achieve greater detection rates with numbers of eigenfaces greater than the number needed for stability without blurring.