Table 2.
Comparison of different methods applied on the three heading stages.
| Decorrelation pre-processing | Feature extraction | Coding method | Spatial pyramid | Vocabulary length | Accuracy Z5.0 (%) | Accuracy Z5.3–Z5.7 (%) | Accuracy ≥ Z5.9 (%) |
|---|---|---|---|---|---|---|---|
| Yes | SIFT | LLC | Yes | 2,000 | 95.24 | 97.79 | 99.59 |
| No | SIFT | LLC | Yes | 2,000 | 57.29 | 82.20 | 85.38 |
| Yes | SIFT | k-NN | Yes | 2,000 | 90.54 | 94.48 | 96.97 |
| Yes | SIFT | LLC | No | 2,000 | 92.90 | 96.54 | 96.90 |
| Yes | SURF | LLC | Yes | 2,000 | 56.84 | 71.55 | 78.45 |
| Yes | SIFT | LLC | Yes | 1,000 | 93.91 | 97.52 | 98.91 |
| Yes | SIFT | LLC | Yes | 1,500 | 94.61 | 97.64 | 99.24 |
| Yes | SIFT | LLC | Yes | 2,500 | 94.90 | 97.59 | 99.49 |