# Survey on Implementations of Generative Adversarial Networks for Semi-Supervised Learning

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Common Techniques Used in Semi-Supervised Learning

#### 2.1. Consistency Regularization

#### 2.2. Pseudo-Labeling

^{3}-CGAN model; pseudo-labeling was used to assign labels to the unlabeled classes.

#### 2.3. Entropy Minimization

## 3. Literature Review of GANS for SSL

#### 3.1. Taxonomy

^{3}-CGAN [28], and EC-GAN [37]. A third approach consisted of models using encoder-based approaches where an encoder was added to the GAN architecture to map images into a latent space, which then subsequently helped in the training process. This approach was seen in BiGAN [38], ALI [39], and Augmented BiGAN [40] models. More recent approaches have used manifold regularization techniques in order to make the model more resistant to perturbations in the input. Laplacian-based GAN [41], Monte Carlo-based GAN [42], SelfAttentionGAN [43], and SSVM-GAN [44] all fall into this category. Other unique approaches involved using two GANs as seen in MCGAN [45], VTGAN [46], and IAGAN [47], and finally leveraging conditional GANs in a stacked discriminator approach, seen in SS-GAN [48], to discriminate between predicted attributes.

#### 3.2. Notation

#### 3.3. Extensions Using Pseudo-Labeling and Classifiers

#### 3.4. Encoder-Based Approaches

#### 3.5. The TripleGAN Approach

_{u},P(c)) using pseudo-labeling.

^{3}-CGAN [28] was another GAN architecture based on Δ-GAN. This architecture was based on the observation that the classification network often gives incorrect yet confident predictions on unlabeled data while generating pseudo-labels. Furthermore, due to the imbalance between real and fake samples, the discriminator learns the real samples and rejects any unseen data even if they are real. The authors proposed using a regularization approach based on Random Regional Replacement in the learning process of the classification and discriminative networks. They implemented two discriminative networks in addition to the classifier and the generator. Fake sample pairs of two types were used, one consisting of synthesized data paired with the target label, and the other consisting of an unlabeled sample paired with its pseudo-label. One of the discriminators was trained to discriminate between real and fake images, while the other was trained to discriminate between two fake sample types.

#### 3.6. Manifold Regularization-Based Methods

#### 3.7. Two-GAN Approaches

#### 3.8. GAN Using Stacked Discriminator

## 4. Results

## 5. Discussion

#### 5.1. Quantitative Analysis

^{3}-CGAN architecture holds the current state of the art as none of the other papers surveyed had a similar evaluation process or a comparison to this model. A number of interesting aspects of the R

^{3}-CGAN that could have contributed to its success. While the underlying architecture was based on TripleGAN, a Random Regional Replacement regularization was applied by making use of the CutMix mix-sample augmentation technique [51]. This technique has been implemented in non-generative semi-supervised learning techniques in order to achieve consistency regularization with good results. Therefore, its success in a generative architecture suggests adaptation of other semi-supervised learning techniques into GANs as well. It is interesting to note that while R

^{3}-CGAN is seemingly the best performing GAN-based technique currently available, it fades in comparison to non-GAN state of the art SSL techniques such as FixMatch [8], which reported error rates of 4.26% on CIFAR-10 with 4000 labeled samples and 2.28% on SVHN with 1000 labeled samples, in addition to showing a good performance of 11.39% error for CIFAR-10 with only 40 labeled samples and 3.96% for SVHN with 40 labeled samples. Therefore, the gap between GAN-based SSL and other state of the art techniques is apparent, and so it would be interesting to attempt to apply some of the techniques used in other SSL algorithms to GANs in order to unify the enhanced performance seen in the state of the art SSL algorithms with the generative aspect that GANs are known for.

#### 5.2. Qualitative Analysis

## 6. Future Directions

^{3}-CGAN’s usage of CutMix, an interesting direction for research could be the implementation of further semi-supervised methods alongside GANs. While this is not a new concept and work including Chen et al. [20] have previously used SSL algorithms such as MeanTeacher to achieve consistency regularization, however, newer SSL techniques could also be looked into, as well. For example, the idea of automated augmentation techniques like RandAugment [55] and AutoAugment [56] used by state of the art SSL techniques like UDA [57] and FixMatch [8] can be explored. Another interesting direction could be the unifying of the current dominant GAN-based SSL techniques by adding manifold regularization to the R

^{3}-CGAN implementation of TripleGAN. Since both techniques have the best results in recent works, combining them could be a step forward in the area of GAN-based SSL. On a similar note, future work can be carried out towards unifying the contrasting approaches of preparing a bad GAN for classification with approaches aiming to simultaneously improve both aspects of the GAN. This is a promising direction as BadGAN approaches have been noted to perform better for larger amounts of data, while GoodGAN approaches have outperformed for smaller levels of data. A unified method would be able to take advantage of these to form a more robust model.

## 7. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 8.**Examples of images generated by good and bad GANs [55].

Term | Definition |
---|---|

x | Original labeled data points |

y | Original labels |

x_{u} | Unlabeled data points |

y’ | Labels of generated data |

z | Randomly generated latent space |

G(z) | Generator |

E(z) | Encoder |

D | Discriminator |

C | Classifier |

P(y) | Probability—Discriminator output |

P(c) | Probability—Classifier output |

H(x) | Entropy of a given distribution over data x |

${\mathrm{E}}_{\mathrm{x}~{\mathrm{p}}_{\mathrm{data}\left(\mathrm{x}\right)}}$ | $\mathrm{Expected}\text{}\mathrm{value}\text{}\mathrm{given}\text{}\mathrm{x}\text{}\mathrm{distributed}\text{}\mathrm{as}\text{}{\mathrm{p}}_{\mathrm{data}\left(\mathrm{x}\right)}$ |

$\parallel \mathrm{f}{\parallel}_{\mathrm{L}}^{2}$ | Laplacian Norm |

Citation | Authors | Date of Publication | Proposed Model | Baseline Models |
---|---|---|---|---|

[49] | Goodfellow et al. | June 2014 | GAN (Original) | n/a |

[30] | J. Springenberg | April 2016 | CatGAN (Categorical) | MTC, PEA, PEA+, VAE + SVM, SS-VAE, Ladder T-model, Ladder-full |

[32] | Salimans et al. | June 2016 | Improved GAN | DGN, Virtual Adversarial, CatGAN, Skip Keep Generative Model, Ladder network, Auxiliary Deep Generative Model |

[31] | A. Odena | October 2016 | SGAN (Semi-Supervised) | CNN (isolated classifier, unspecified) |

[29] | Dai et al. | November 2017 | GoodBadGAN | CatGAN, SDGM, Ladder network, ADGM, FM, ALI, VAT small, TripleGAN, Π model, VAT + EntMin + Large |

[19] | Wei et al. | March 2018 | CT-GAN | Ladder, VAT, CatGAN, Improved GAN, TripleGAN |

[33] | Sun et al. | October 2020 | MatchGAN | StarGAN |

Citation | Authors | Date of Publication | Proposed Model | Baseline Models |
---|---|---|---|---|

[38]. | Donahue et al. | May 2016 | BiGAN | - |

[39] | Dumoulin et al. | February 2017 | ALI (Adversarially Learned Inference) | CIFAR-10: Ladder network, CatGAN, GAN (Salimans 2016); SVHN: VAE, SWWAE, DCGAN + L2SVM, SDGM, GAN (Salimans 2016) |

[40] | Kumar et al. | December 2017 | Augmented BiGAN |

Citation | Authors | Date of Publication | Proposed Model | Baseline Models |
---|---|---|---|---|

[26] | Li et al. | November 2017 | TripleGAN | M1 + M2, VAT, Ladder, Conv-Ladder, ADGM, SDGM, MMCVA, CatGAN, Improved GAN, ALI |

[35] | Gan et al. | November 2017 | TriangleGAN | CatGAN, Improved GAN, ALI, TripleGAN |

[36] | Deng et al. | November 2017 | SGAN (Structured) | Ladder, VAE, CatGAN, ALI, Improved GAN, TripleGAN |

[27] | J. Dong and T. Lin | November 2019 | MarginGAN | NN, SVM, CNN, TSVM, DBN-rNCA, EmbedNN, CAE, MTC |

[34] | Wu et al. | January 2020 | EnhancedTGAN (Triple) | Ladder network, SPCTN, Π model, Temporal Ensembling, Mean Teacher, VAT, VAdD, VAdD + VAT, SNTG + Π model, SNTG + VAT, CatGAN, Improved GAN, ALI, TripleGAN, GoodBadGAN, CT-GAN, TripleGAN |

[28] | Liu et al. | August 2020 | R^{3}-CGAN (Random Regional Replacement Class-Conditional) | Ladder network, SPCTN, Π model, Temporal Ensembling, Mean Teacher, VAT, VAdD, SNTG + Π model, Deep Co-Train, CCN, ICT, CatGAN, Improved GAN, ALI, TripleGAN, Triangle-GAN, GoodBadGAN, CT-GAN, EnhancedTGAN |

[43] | A. Haque | March 2021 | EC-GAN (External Classifier) | DCGAN |

Citation | Authors | Date of Publication | Proposed Model | Baseline Models |
---|---|---|---|---|

[41] | Lecouat et al. | May 2018 | Laplacian-based GAN | Ladder network, Π model, VAT, VAT + EntMin, CatGAN, Improved GAN, TripleGAN, Improved semi-GAN, Bad GAN |

[42] | Lecouat et al. | July 2018 | Monte Carlo-based GAN | Π model, Mean Teacher, VAT, Vat + EntMin, Improved GAN, Improved Semi-GAN, ALI, TripleGAN, Bad GAN, Local GAN |

[43] | Xiang et al. | November 2019 | SelfAttentionGAN | CatGAN, Improved GAN, TripleGAN, Bad GAN, Local GAN, Manifold-GAN, CT-GAN, Ladder network, π-model, Temporal Ensembling w/augmentation, VAT + EntMin w/ aug, MeanTeacher, MeanTeacher w/aug, VAT + Ent + SNGT w/aug |

[44] | Tang et al. | August 2020 | SSVM-GAN (Scalable SVM) | Ladder Network, CatGAN, ALI, VAT, FM GAN, Improved FM, GAN, TripleGAN, Π model, Bad GAN |

Citation | Authors | Date of Publication | Proposed Model | Baseline Models |
---|---|---|---|---|

[48] | Sricharan et al. | August 2017 | SS-GAN (Semi-Supervised) | C-GAN (conditional GAN on full dataset), SC-GAN (conditional GAN only on labeled dataset), AC-GAN (supervised auxiliary classifier GAN on full dataset), SA-GAN (semi-supervised AC-GAN) |

[47] | Motamed et al. | January 2021 | IAGAN (Inception-Augmentation) | AnoGAN, AnoGAN w/traditional augmentation, DCGAN |

[45] | S. Motamed and F. Khalvati | February 2021 | MCGAN (Multi-Class) | DCGAN |

[46] | S. Motamed and F. Khalvati | March 2021 | VTGAN (Vanishing Twin) | OC-SVM, IF, AnoGAN, NoiseGAN, Deep SVDD |

Citation | Proposed Model | Datasets Evaluated On | Results |
---|---|---|---|

[49] | GAN (Original) | MNIST, TFD | Gaussian Parzen window: MNIST: 225, TDF: 2057 |

[30] | CatGAN (Categorical) | MNIST | 1.91% PI-MNIST test error w/100 labeled examples, outperforms all models except Ladder-full (1.13%) |

[32] | Improved GAN | MNIST, CIFAR-10, SVHN | MNIST: 93 incorrectly predicted test examples w/ 100 labeled samples, outperforms all other; CIFAR-10: 18.63 test error rate w/4000 labeled samples, outperforms all other; SVHN: 8.11% incorrectly predicted test examples w/1000 labeled samples, outperforms all other |

[31] | SGAN (Semi-Supervised) | MNIST | 96.4% classifier accuracy w/1000 labeled samples, comparable to isolated CNN classifier (96.5%) |

[29] | GoodBadGAN | MNIST, SVHN, CIHAR-10 | MNIST: 79.5 # of errors, outperforms all; SVHN: 4.25% errors, outperforms all; CIFAR-10: 14.41% errors, outperforms all except Vat + EntMin + Large |

[19] | CT-GAN | MNIST | 0.89% error rate, outperformed all |

[33] | MatchGAN | CelebA, RaFD | (For both datasets, 20% of training data labeled) CelebA: 6.34 FID, 3.03 IS; RaFD: 9.94 FID, 1.61 IS; outperformed StarGAN in all metrics |

Citation | Proposed Model | Datasets Evaluated On | Results |
---|---|---|---|

[38] | BiGAN | ImageNet | Max Classification accuracy: 56.2% with conv classifier |

[39] | ALI (Adversarially Learned Inference) | CIFAR-10, SVHN, CelebA, ImageNet (center-cropped 64 × 64 version) | CIFAR-10: 17.99 misclassification rate w/4000 labeled samples, outperforms all; SVHN: 7.42 misclassification rate w/1000 labeled samples, outperforms all |

[40] | Augmented BiGAN | SVHN, CIFAR-10 | SVHN: 4.87 test error w/500 labeled, 4.39 test error w/1000 labeled, outperforms all for both; CIFAR-10: 19.52 test error w/1000 labeled, outperforms all, 16.20 test error w/4000 labeled, outperforms all except Temporal Ensembling |

Citation | Proposed Model | Datasets Evaluated On | Results |
---|---|---|---|

[26] | TripleGAN | MNIST, SVHN, and CIFAR-10 | MNIST: 0.91% error rate w/100 labeled samples, outperforms all except Conv-Ladder; SVHN: 5.77% error rate w/1000 labeled samples, outperforms all except MMCVA; CIFAR-10: 16.99% error rate w/4000 labeled samples, outperforms all |

[35] | Triangle-GAN | CIFAR-10 | 16.80% error rate w/4000 labeled samples, outperforms all |

[36] | SGAN (Structured) | MNIST, SVHN, CIFAR-10 | MNIST: 0.89% error rate w/100 labeled, outperforms all but equal as Ladder; SVHN: 5.73% error rate w/1000 labeled, outperforms all; CIFAR-10: 17.26% error rate w/4000 labeled, outperforms all |

[27] | MarginGAN | MNIST | 2.06% error rate w/3000 labels, outperformed all |

[34] | EnhancedTGAN (Triple) | MNIST, SVHN, CIFAR-10 | MNIST: 0.42% error rate w/100 labels, outperforms all; SVHN: 2.97% error rate w/1000 labels, outperforms all; CIFAR-10: 9.42% error rate w/4000 labels, outperforms all |

[28] | R^{3}-CGAN (Random Regional Replacement Class-Conditional) | SVHN, CIFAR-10 | SVHN: 2.79% error rate w/1000 labels, outperformed all except equal with EnhancedTGAN; CIFAR-10: 6.69% error rate w/4000 labels, outperformed all |

[43] | EC-GAN (External Classifier) | SVHN, X-ray Dataset | SVHN: 93.93% accuracy w/25% of dataset, outperformed DCGAN; X-ray: 96.48% accuracy w/25% of dataset, outperformed DCGAN |

Citation | Proposed Model | Datasets Evaluated On | Results |
---|---|---|---|

[41] | Laplacian-based GAN | SVHN, CIFAR-10 | SVHN: 4.51% error rate w/1000 labeled, outperformed all except Vat + EntMin, Improved semi-GAN, and Bad GAN; CIFAR-10: 14.45% error rate w/4000 labeled, outperformed all except Vat + EntMin and Bad GAN |

[42] | Monte Carlo-based GAN | CIFAR-10, SVHN | CIFAR-10: 14.34% error rate w/4000 labels, outperformed all except VAT, VAT + EntMin, and Local GAN; SVHN: 4.63% error rate w/1000 labels, outperformed VAT + EntMin and Improved semi-GAN |

[43] | SelfAttentionGAN | SVHN, CIFAR-10 | CIFAR-10: 9.87% error rate w/4000 labels, outperformed all; SVHN: 4.30% error rate w/1000 labels, outperformed all except Bad GAN, VAT + EntMin w/aug, MeanTeacher w/aug, VAT + Ent + SNGT w/aug |

[44] | SSVM-GAN (Scalable SVM) | CIFAR-10, SVHN | CIFAR-10: 14.27% error rate w/4000 labels, outperformed all; SVHN: 4.54% error rate w/1000 labels, outperformed all except Bad GAN |

Citation | Proposed Model | Datasets Evaluated on | Results |
---|---|---|---|

[48] | SS-GAN (Semi-Supervised) | MNIST, CelebA, CIFAR-10 | MNIST: 0.1044 class prediction error, outperforms only SA-GAN, 0.0160 reconstruction error, outperforms SA-GAN and SC-GAN (both metrics w/20 labeled samples); CelebA: 0.040 reconstruction error, outperforms all except C-GAN; CIFAR-10: 0.299 class pred error, outperforms only AC-GAN and SC-GAN, 0.061 recon error, outperforms all except C-GAN |

[47] | IAGAN (Inception-Augmentation) | Pneumonia X-rays: Dataset I (3765 imgs), Dataset II (4700 imgs) | Dataset I: 0.90 AUC, outperformed all; Dataset II: 0.76 AUC, outperformed all |

[45] | MCGAN (Multi-Class) | MNIST, F-MNIST | MNIST: 0.9 AUC unknown class classification and 0.84 known class classification, outperformed DCGAN; F-MNIST: 0.79 AUC unknown & 0.65 known, outperformed DCGAN |

[46] | VTGAN (Vanishing Twin) | MNIST, F-MNIST | MNIST: 0.90, 0.92, 0.85, and 0.86 AUC, outperformed all in all 4 experiments; F-MNIST: 0.87, 0.76, 0.70, 0.57, 0.62, 0.70 AC, outperformed all in 4 out of 6 experiments |

Citation | Category | Proposed Model | Results |
---|---|---|---|

[30] | Pseudo-labeling and Classifiers | CatGAN | 1.91% PI-MNIST test error w/100 labeled examples, outperforms all models except Ladder-full (1.13%) |

[39] | Encoder-based | ALI | CIFAR-10: 17.99 misclassification rate w/4000 labeled samples, outperforms all; SVHN: 7.42 misclassification rate w/1000 labeled samples, outperforms all |

[26] | TripleGAN | TripleGAN | MNIST: 0.91% error rate w/100 labeled samples, outperforms all except Conv-Ladder; SVHN: 5.77% error rate w/1000 labeled samples, outperforms all except MMCVA; CIFAR-10: 16.99% error rate w/4000 labeled samples, outperforms all |

[44] | Manifold Regularization | SSVM-GAN | CIFAR-10: 14.27% error rate w/4000 labels, outperformed all; SVHN: 4.54% error rate w/1000 labels, outperformed all except Bad GAN |

[28] | TripleGAN | R^{3}-CGAN | SVHN: 2.79% error rate w/1000 labels, outperformed all except equal with EnhancedTGAN; CIFAR-10: 6.69% error rate w/4000 labels, outperformed all |

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## Share and Cite

**MDPI and ACS Style**

Sajun, A.R.; Zualkernan, I.
Survey on Implementations of Generative Adversarial Networks for Semi-Supervised Learning. *Appl. Sci.* **2022**, *12*, 1718.
https://doi.org/10.3390/app12031718

**AMA Style**

Sajun AR, Zualkernan I.
Survey on Implementations of Generative Adversarial Networks for Semi-Supervised Learning. *Applied Sciences*. 2022; 12(3):1718.
https://doi.org/10.3390/app12031718

**Chicago/Turabian Style**

Sajun, Ali Reza, and Imran Zualkernan.
2022. "Survey on Implementations of Generative Adversarial Networks for Semi-Supervised Learning" *Applied Sciences* 12, no. 3: 1718.
https://doi.org/10.3390/app12031718