1.1 Experimental Results
The investigation has been prepared using MATLAB 2021b. The primary objective of this study is to propose a new method for selecting features and to identify grapevine leaves types using hybrid algorithms that have been developed. First and foremost, the dataset is acquired from the public website, as indicated in the dataset section. The following models, namely DarkNet-53, GoogleNet, NasNetMobile, InceptionResNet_v2, and ResNet-18, are utilized as automatic feature extractors using a 5-fold cross-validation and transfer learning approach, each model being evaluated individually. In the subsequent procedure, we derive feature weights from the final layer of the relevant architecture. Subsequently, the features are chosen using recommended techniques: ERSS, MERSS, RSS, and SRS. In the meantime, we employ ANN to classify all the selected features. Table 4 demonstrates the performance of these pre-trained architectures in classifying grapevine leaf images through the utilization of 5-fold cross-validation.
Table 4
Performance of pre-trained architectures on grapevine leaf images using 5-fold cross validation.
Architecture | Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
DarkNet-53 | 0.9620 | 0.9620 | 0.9761 | 0.9621 | 0.8812 | 0.9990 |
GoogleNet | 0.8600 | 0.8600 | 0.9109 | 0.8603 | 0.5625 | 0.9788 |
InceptionResNet_v2 | 0.8980 | 0.8980 | 0.9354 | 0.8980 | 0.6812 | 0.9858 |
NASNetMobile | 0.8820 | 0.8820 | 0.9520 | 0.8816 | 0.6312 | 0.9762 |
ResNet-18 | 0.9500 | 0.9500 | 0.9686 | 0.9500 | 0.8437 | 0.9974 |
Based on the data presented in Table 4, it can be observed that the utilization of pre-trained architectures has resulted in highly successful performances. The empirical findings suggest that DarkNet-53 achieves the most optimal performance, exhibiting an accuracy rate of 96.20% during this particular stage. The second model is ResNet-18, which exhibits a commendable accuracy of 95%. Following the series of performances, InceptionResNet_v2, NASNetMobile, and GoogleNet exhibit accuracies of 89.8%, 88.2%, and 86% in that order.
Despite the satisfactory nature of the performances, we employ the feature selection technique and machine learning algorithm to ascertain the credibility of the research findings. In the current phase of this study, we have partitioned the dataset into a 70% training subset and a 30% testing subset subsequent to training the dataset using the relevant architecture. Subsequently, we extract features from the last layer (which varies depending on the specific architecture) and subsequently employ our proposed methodologies, namely ERSS, MERSS, RSS, and SRS, to select the desired features. The classification stage has commenced using an ANN, and we have evaluated all hybrid structures. The outcomes of these evaluations have been documented in Table 5–9.
When extracting features from DarkNet-53, it has been observed that the global average pooling layer, commonly referred to as 'gap', proves to be beneficial. A total of 1024 features are acquired from the layer, and a subset of 36 features is selected using the ERSS, RSS, and SRS techniques. Furthermore, a total of 45 significant features have been determined using the MERSS method. The output is presented in Table 5.
Table 5
Hybrid algorithm performance with DarkNet53, suggested methods, and ANN.
Hybrid Algorithm | Test Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
DarkNet53-ERSS-ANN | 0.9533 | 0.9533 | 0.9707 | 0.9533 | 0.8542 | 0.9956 |
DarkNet53-RSS-ANN | 0.9333 | 0.9333 | 0.9580 | 0.9339 | 0.7917 | 0.9942 |
DarkNet53-MERSS-ANN | 0.9733 | 0.9733 | 0.9833 | 0.9733 | 0.9167 | 0.9925 |
DarkNet53-SRS-ANN | 0.8400 | 0.8400 | 0.8980 | 0.8391 | 0.5000 | 0.9633 |
Based on the findings presented in Table 5, the application of our proposed methodologies yields efficient results. It is worth noting that the performances obtained are in the form of test results. We are pleased to report that these results exhibit a high level of confidence in accurately identifying different types of grapevine leaf. The DarkNet53-MERSS-ANN algorithm has achieved the highest test accuracy of 97.33% along with other metrics. Additionally, the kappa value approaches 1, indicating that the algorithm can be considered highly successful. Furthermore, the performance is enhanced with the proposed methodology. In the previous iteration, the DarkNet-53 model demonstrated a classification accuracy of 96.20%. Furthermore, the algorithm employed in this study yields the utmost test accuracy when tasked with classifying grapevine leaf images. Additionally, Fig. 3 depicts the confusion matrix obtained from the DarkNet53-MERSS-ANN algorithm.
The following model in consideration is GoogleNet. If features are extracted from the GoogleNet model, the average pooling layer, specifically named 'pool5-7x7_s1', is observed to be useful. Indeed, a total of 1024 features are extracted from the layer, and subsequently, a selection process is performed using ERSS, RSS, and SRS techniques to identify the most significant 36 features. Furthermore, a total of 45 significant features have been identified using the MERSS method. The output of the computation is displayed in Table 6.
Table 6
Hybrid algorithm performance with GoogleNet, suggested methods, and ANN.
Hybrid Algorithm | Test Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
GoogleNet-ERSS-ANN | 0.9400 | 0.9400 | 0.9622 | 0.9402 | 0.8125 | 0.9892 |
GoogleNet -RSS-ANN | 0.9533 | 0.9533 | 0.9707 | 0.9533 | 0.8542 | 0.9946 |
GoogleNet -MERSS-ANN | 0.9400 | 0.9400 | 0.9622 | 0.9388 | 0.8125 | 0.9897 |
GoogleNet -SRS-ANN | 0.9067 | 0.9067 | 0.9410 | 0.9051 | 0.7083 | 0.9822 |
Table 6 indicates that the GoogleNet-RSS-ANN algorithm, with a test accuracy of 95.33%, is the most accurate of the methods we have proposed. The values for the sensitivity, G-Mean, F-measure, kappa value, and AUC are 95.33%, 97.07%, 0.9533, 0.8542, and 0.9946, respectively. In addition, the kappa value is close to 1, which indicates that the algorithm is quite successful. Moreover, the performance is enhanced by the suggested method. Previously, the accuracy of GoogleNet was 86%.
The model is referred to as NasNetMobile. If it's desired to collect features from NasNetMobile, it is possible to employ a global average pooling layer, denoted as 'global_average_pooling2d_1'. A total of 1056 features have been extracted from the layer, and a subset of 36 feature is selected using the ERSS, RSS, and SRS methods. Additionally, the MERSS method is utilized to identify a total of 45 crucial features. The outcomes are presented in Table 7.
Table 7
Hybrid algorithm performance via NasNetMobile, suggested methods, and ANN.
Hybrid Algorithm | Test Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
NasNetMobile -ERSS-ANN | 0.7333 | 0.7333 | 0.8273 | 0.7339 | 0.1667 | 0.9186 |
NasNetMobile -RSS-ANN | 0.7733 | 0.7733 | 0.8541 | 0.7730 | 0.2917 | 0.8914 |
NasNetMobile -MERSS-ANN | 0.7933 | 0.7933 | 0.8674 | 0.7894 | 0.3542 | 0.9375 |
NasNetMobile -SRS-ANN | 0.7067 | 0.7067 | 0.8092 | 0.7077 | 0.0833 | 0.9099 |
Table 7 shows that the NasNetMobile-MERSS-ANN algorithm outperforms our suggested methods, with a test accuracy of 79.33%. Furthermore, its sensitivity, G-Mean, F-measure, kappa value, and AUC are 79.33%, 86.74%, 0.7894, 0.3542, and 0.9375, respectively. When the kappa value is compared to one, it indicates that the algorithm is not preferable. NasNetMobile previously had an accuracy of 88.20%.
The one after that is InceptionResNet_v2. If features are obtained from it, a global average pooling layer known as 'avg-pool' is found to be useful. Essentially, 1536 features are extracted from the layer, with significant 53 features selected using the ERSS, RSS, and SRS methods. The MERSS method also identifies 55 essential features. Table 8 displays all of the results.
Table 8
Hybrid algorithm performance using InceptionResNet, suggested methods, and ANN.
Hybrid Algorithm | Test Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
InceptionResNet -ERSS-ANN | 0.9267 | 0.9267 | 0.9538 | 0.9266 | 0.7708 | 0.9953 |
InceptionResNet -RSS-ANN | 0.9000 | 0.9000 | 0.9367 | 0.8995 | 0.6875 | 0.9972 |
InceptionResNet -MERSS-ANN | 0.9267 | 0.9267 | 0.9538 | 0.9267 | 0.7708 | 0.9842 |
InceptionResNet -SRS-ANN | 0.8400 | 0.8400 | 0.8980 | 0.8418 | 0.5000 | 0.9811 |
Table 8 shows that when using our recommended techniques, two algorithms—InceptionResNet-ERSS-ANN and InceptionResNet-MERSS-ANN—perform best, with test accuracy of 92.67%. Additionally, they achieve the same ratio for their sensitivity, G-Mean, F-measure, kappa value, and AUC, which are 92.67%, 95.38%, 0.9266, 0.7708, and 0.9953, respectively. InceptionResNet previously achieved an accuracy of 89.90%.
ResNet-18 is the last. If features are taken from it, the 'pool5' average pooling layer is discovered to be useful. In essence, 512 features from the layer are collected, and the most significant 24 features are chosen using the ERSS, RSS, and SRS methods. 32 significant features are also found using the MERSS method. Table 9 displays the complete results.
Table 9
Hybrid algorithm performance using ResNet-18, suggested methods, and ANN.
Hybrid Algorithm | Test Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
ResNet18-ERSS-ANN | 0.8000 | 0.8000 | 0.8718 | 0.7988 | 0.3750 | 0.9531 |
ResNet18 -RSS-ANN | 0.8000 | 0.8000 | 0.8718 | 0.7999 | 0.3750 | 0.9626 |
ResNet18 -MERSS-ANN | 0.8533 | 0.8533 | 0.9067 | 0.8531 | 0.5417 | 0.9761 |
ResNet18 -SRS-ANN | 0.7733 | 0.7733 | 0.8541 | 0.7748 | 0.2917 | 0.9472 |
Analyzing our suggested methods, Table 9 shows that ResNet18-MERSS-ANN performs the best, with a test accuracy of 85.33%. Additionally, its sensitivity, G-Mean, F-measure, kappa value, and AUC are all achieved at respective levels of 85.33%, 90.67%, 0.8531, 0.5417, and 0.9761. Prior to this, ResNet18 has a 95% accuracy rate.
In recent years, numerous researchers have employed various feature selection methods in their studies(Chandrashekar and Sahin, 2014, Ozaltin et al., 2022, Koklu et al., 2022). However, the process of identifying the suitable feature selection is not straightforward, as certain methods may rely on underlying assumptions. This study proposes several practical methods and conducts a comparison with Neighborhood Component Analysis (NCA), a non-parametric method that operates without making any assumptions. The results of applying various combinations of NCA are presented in Table 10
Table 10
Performance of hybrid algorithm based on NCA and ANN combination.
Algorithm | Accuracy | Sensitivity | G-Mean | F-measure | Kappa | AUC |
DarkNet53-NCA-ANN | 0.9667 | 0.9667 | 0.9790 | 0.9664 | 0.8958 | 1.00 |
GoogleNet NCA-ANN | 0.9333 | 0.9333 | 0.9580 | 0.9329 | 0.7917 | 0.9858 |
InceptionResNet -NCA-ANN | 0.8800 | 0.8800 | 0.9239 | 0.8790 | 0.6250 | 0.9911 |
NASNetMobile-NCA-ANN | 0.7000 | 0.7000 | 0.8047 | 0.6953 | 0.0625 | 0.8690 |
ResNet18- NCA-ANN | 0.8133 | 0.8133 | 0.8805 | 0.8126 | 0.4167 | 0.9778 |
Based on the findings presented in Table 10, it can be observed that DarkNet53-NCA-ANN emerges as the most effective feature selection method, exhibiting a notable accuracy rate of 96.67%. In addition, the sensitivity, G-Mean, F-measure, kappa value, and AUC of the system were determined to be 96.67%, 97.90%, 0.9664, 0.8958, and 1.00, respectively. The confusion matrix of the DarkNet53-NCA-ANN model is depicted in Fig. 4.
DarkNet-53 architecture is employed as a deep feature extractor for grapevine leaf images. To enhance the performance of the feature extraction process, the most effective feature selection method, known as MERSS, is utilized. Through the application of MERSS on the extracted features, a notable accuracy rate of 97.33% is achieved. In contrast to NCA, MERSS demonstrates superior performance. Hence, it can be asserted that the feature selection method we have developed exhibits the highest level of performance.
The deep feature extractor GoogleNet is used for the purpose of extracting features from grapevine leaf images. The feature selection method that yields successful results is RSS, which is applied to the extracted features. This method achieves an accuracy of 95.33%. When comparing it to NCA, it exhibits inferior performance in comparison to RSS. Our model, GoogleNet, consistently outperforms other models, making it the optimal choice.
InceptionResNet_v2 is implemented as a deep feature extractor for grapevine leaf images. The successful feature selection methods employed are MERSS and ERSS, which operate on the features and achieve a hit accuracy of 92.67%. When comparing it to NCA, it performs worse than MERSS and ERSS. Our model, InceptionResNet_v2, is the best one to use.
NasNetMobile operates as a deep feature extractor for grapevine leaf images. The top feature selection method used is MERSS, which is applied to the extracted features. This method resulted in an accuracy of 79.33%. When comparing it to NCA, MERSS exhibits better performance. In conclusion, when utilizing NasNetMobile, our solution proves to be the most effective once again.
ResNet18 is utilized as a deep feature extractor for grapevine leaf images. The feature selection method employed was MERSS, which was applied to the extracted features. This approach resulted in an accuracy of 85.33%. When comparing it to NCA, MERSS has lower performance. Once again, when utilizing ResNet-18, we eventually have the best one. Based on the results, it can be concluded that MERSS performs well after implementing deep feature extractors. Additionally, it has been mentioned earlier that MERSS is superior to NCA.