An Enhanced GAN for Image Generation

1  Introduction

Due to the development of image vision techniques, image generation techniques have been applied in many fields, i.e., person privacy protection [1] and entertainment [2]. That is, digital devices can use generated face rather than captured unauthorized faces to address personal privacy protection questions [1]. Image generation techniques [2] can generate virtual persons rather than spokesmen in entertainment to save costs. Traditional image generation techniques can use multiple two-dimensional images to recover three-dimensional structures to achieve a transform of multiple images to one aim image [3]. For instance, three-dimensional morphable model uses principal component analysis to decrease texture and facial shape features in low-dimensional space to generate more real face images [3]. However, it requires a lot of varying illuminations, postures, and expressions, which may cause high data collection costs and low of the proposed method. GANs with generating high-quality and diverse images have become popular in image generation [4]. Designed two different encoders in an unsupervised way can learn potential distribution to address attribute entanglement, where output distribution can use adversarial strategy learning to maintain characteristic features of GAN to improve the effect of image generation [5]. Using ResNet feature pyramid as an encoder network can extract style from three features with different scales, and then a mapping network is used to extract learned styles from corresponding images in image generation [6]. Alternatively, an iterative feedback mechanism is used to improve the generation quality of face images to keep a balance between image fidelity and editing ability. To improve the quality of image generation, a residual learning is used in a transfer process to improve the iterative feedback mechanism [7]. Using compute similarity between potential vectors and images to design an adaptive similarity encoder to generate high-fidelity images, which can use existing encoders into different GANs to generate images [8]. To improve performance of image generation without increasing computational costs, multi-layer losses of ID and facial analysis are referred to generate more detailed information for image generation [9]. Alternatively, Xu et al. [10] used a novel hierarchical encoder to extract hierarchical features via input images to improve the effects of generated images. Although mentioned gametic GANs may improve the effects of generated images, they may suffer from challenges from varying scenes.

In this paper, we present an enhanced GAN via improving a generator for image generation termed as EIGGAN. EIGGAN utilizes a spatial attention mechanism to improve the generator in order to extract salient information that can enhance the correctness of the predicted images. To improve the generation effects, parallel residual operations are gathered into a generation network to extract more structural information from the different layers in terms of their relation to context. To make a tradeoff between speed and accuracy in image generation, a mixed loss function is used in a GAN to generate more realistic images. Experiments illustrate that the proposed EIGGAN is competitive in terms of the metrics: Frechet Inception Distance (FID) [11], Learned Perceptual Image Patch Similarity (LPIPS) [12], Multi-Scale Structural Similarity Index Measure (MS-SSIM) [13], Kernel Inception Distance (KID) [14], Number of statistically-Different Bins (NDB) [15] and Inception Score (IS) [16] for image generation.

The contributions of this paper can be summarized as follows:

1.    A spatial attention mechanism is employed to improve the generation to facilitate more salient information, enhancing the truthfulness of the generated images.

2.    Parallel residual operations are used to extract more complementary and structural information with a spatial attention mechanism to improve the effects of image generation, according to its relation to context.

3.    A mixed loss is applied to generate more realistic images.

The remaining parts of this paper are conducted as follows. Section 2 presents related work. Section 3 gives the proposed method. Section 4 provides experimental analysis and results. Section 5 summarizes the whole paper.

2  Related Work

GANs with strong generative abilities are used for image generation in generation [17]. To improve generation effects, designing novel network architectures can improve GANs as the popular way of image generation [17]. It can be summarized into two kinds: improved common GANs and StyleGANs. The first method usually improves a generator or discriminator to improve the learning abilities of GANs for image generation. For improving a generator, asymmetric network architectures between a generator and discriminator are designed to address image content differences between input and outputs to promote the effects and performance of image-to-image translation [17]. To address native relation effect of semantic and latent space, a combination of a pretrain GAN and prior knowledge is used to extract latent semantic from architecture attributes in shallow layers and in apparent deep layers to improve the quality of generation images [18]. Alternatively, zooming areas of training data in image representation space in a discriminator can easily train a GAN to generate images [19]. To address dense visual alignment questions, a spatial Transformer is used to map random samples to a joint object mode for image generation [20]. To edit more attributions of generated images, the second method based on StyleGANs is proposed.

That is, a StyleGAN compares a learnable intermediate latent space W and standard Gaussian latent space to the reflected distribution of training data and they can effectively code rich semantic information to change the attribution of generated images, i.e., expressions and illuminations in image generation [21]. To better address image generation tasks, the second method uses fine-tuning styleGANs to enhance the quality of generation images [22]. To address inverse mapping questions of high-quality reconstruction, editability and fast reference, hypernetworks are proposed [16]. A two-phase mechanism was conducted as follows. The first phase was used to train an encoder to map an input image to a latent space. The second phase utilized a hypernetwork to recover lost information from the first phase to image editing [22]. A hypernetwork can be used to tune the weights of StyleGAN to better express given images in editable areas from the latent space for image editing [23]. To address domain transfer of image generation, a simple feature match loss is gathered into a StypleGAN to improve generation quality with less computational costs [24]. To avoid the collapse of latent variants in StyleGAN, a class embedding enhancement mechanism is referred to a self-supervised learning based on a latent space to reduce the relation of latent variants to improve the results of image generation [25]. Although these methods can improve the effects of image generation, StyleGANs refer to more training time and higher computational costs. To better generate images, a Progressive Growing of Generative Adversarial Networks (PGGAN) uses a progressively large model to reduce training difficulty to generate smoother and continuous images [26]. Inspired by that, we use a PGGAN to improve a GAN for image generation in this paper.

3  Proposal Method

3.1 Network Architecture

To better generate high-quality images, we designed an enhanced GAN to improve a generator in image generation (EIGGAN) in Fig. 1. EIGGAN mainly uses a generator and a discriminator to game to generate high-quality images. To enhance the robustness of gamistic generator and discriminator in varying scenes, an improved generator is developed. To generate more real images, three operations are affected on a generation network. The first operation is that a parallel residual learning operation is used to extract more structural information of different layers in terms of relation of context. To enhance the truthfulness of generating images, a spatial attention mechanism is gathered into this generation network to extract more salient information to improve the effect of image generation. The third operation utilizes a mixed loss function to update the parameters of a GAN to balance speed and accuracy in image generation. More detailed information on the generation network can be shown as follows.

Figure 1: Network architecture of EIGGAN

The generation network is composed of five components, i.e., Transpose ConvBlock, Residual ConvBlock, 2X Upsampling, Attention ConvBlock, Equalized Conv operation. The Transpose ConvBlock [26] is set to the first layer, which can convert a noisy vector to a matrix. 2X Upsampling is set to the second, fourth and sixth layers to enlarge obtained feature mapping to capture more context information. Enhanced Residual ConvBlock is set to the third and fifth layers to extract more structural information from different layers in terms of relation to context. An enhanced attention ConvBlock is set to the sixth layer to extract more salient information for image generation. An Equalized Conv [26] is used as the last layer to normalize obtained features to accelerate training speed. To clearly express the mentioned process, the following equation can be conducted.

Og=G(z)=EC(EAC(Up(ERC(Up(ERC(Up(TC(z))))))))(1)

where z is random noise, G is a function of a generation network, Og is an output of the generation network. TC denotes a function of a Transpose ConvBlock, ERC denotes a function of an enhanced residual ConvBlock. Up denotes a 2X upsampling operation. EC denotes a function of an Equalized Conv. Its parameters can be updated by a mixed loss function in Section 3.2.

3.2 Loss Function

To make a tradeoff between performance and speed, a mixed loss is conducted. That is, a mixed loss is composed of normal loss-based GAN [27], non-saturating loss [28] and a combination of R1 [29] and R2 regularization [29]. Non-saturation loss can make a generator more stable in the training process [28]. R1 regularization loss can make a discriminator easier to converge via penalizing gradients of real images to obtain more reliable images [28]. R2 regularization loss can penalty gradients of generating images to easier converge for image generation [29]. Mentioned a loss function is shown as follows.

LD=−1m∑i=1m[log⁡D(x(i))]+[log⁡(1−D(G(z(i))))]+γ2Epϑ+pθ[∇‖Dψ(x)‖ 2]D(G(z))(2)

LG=1m∑i=1m[log⁡(G(z(i)))](3)

where LD is a loss of a discriminator. D(x) denotes probability of real images, where x is a given real image. D(G(z)) denotes probability of generating images, where z is noise. m is a sample minibatch of noise. pϑ is distribution of true images. pθ is distribution of a generator. LG is a loss of a generator.

3.3 Enhanced Residual ConvBlock

Enhanced Residual ConvBlock is used to extract more structural information of different layers for image generation in terms of relation of context as shown in Fig. 1. It is composed of three Equalized Conv, two Leaky ReLU and two PixelNorm. Two combinations of Equalized Conv, Leaky ReLU and PixeNorm are stacked to extract more structural information to improve the effect of image generation. To extract more complementary information, an extra Equalized Conv, an output of the first stacked Equalized Conv, Leaky ReLU and PixelNorm and an output of two stacked Equalized Conv, Leaky ReLU and PixelNorm in a parallel way are gathered to extract more structural information, where a residual learning operation denotes a fusion way. It can be expressed as the following equation:

OERC=ERC(It)=PN(LR(EC(It)))+PN(LR(EC(PN(LR(EC(It))))))+EC(It)(4)

where It is an input of an enhanced residual ConvBlock. OERC is output of an enhanced residual ConvBlock. LR is a function of Leaky ReLU. PN is a function of PixelNorm. + is a residual learning operation.

3.4 Enhanced Attention ConvBlock

An enhanced attention ConvBlock can extract more salient information for image generation. It is composed of four components, i.e., Equalized Conv, Spatial Attention, Leaky ReLU and PixelNorm. It is different from ERresidual Block that spatial attention [30] is set between the first Equalized Conv and Leaky ReLU to extract salient information to improve effect of image generation. This process can be shown as follows:

OEAC=EAC(IEA)=PN(LR(SA(EC(IEA))))+PN(LR(EC(PN(LR(SA(EC(IEA)))))))+EC(IEA)(5)

where IEA is an input of EAttention ConvBlock. OEAC is an output of EResidual ConvBlock. SA denotes a function of spatial attention.

4  Experimental Analysis and Results

4.1 Datasets

Real image datasets are composed of 202,599 face images from CelebA [31] and 60,000 images with ten different categories, i.e., planes, cars, birds, cats, deer, dogs, frogs, horses, ships and trucks from CIFAR-10 [32]. Each image is 32 × 32. Generating image datasets: Each EIGGAN model can generate 10,000 images.

4.2 Experimental Settings

Parameters of training a EIGGAN in image generation are listed as follows. Slope parameter of LeakyReLU is 0.2. λ of regularization parameter is 1 on CelebA and it is 0.1 on CIFAR-10. Batch size is 64. Epoch number on CelebA is 255. Epoch number on CIFAR-10 is 266. Learning rate on CelebA is 0.002, learning rate on CIFAR-10 is 0.001. β1 = 0 and β2 = 0.99. Also, parameters can be optimized by Adam [33]. All the codes implemented by PyTorch 1.13.1, and Python of 3.9.13 run on Ubuntu 20.04.3 with AMD EPYC 7502/3.35 GHz, Central Processing Unit (CPU) of 32 cores, 128 RAM. Also, a Graphics Processing Unit (GPU) of Nvidia GeForce GTX 3090 and Nvidia CUDA 12.2 can be used to improve training speed.

4.3 Experimental Analysis

To improve robustness of GANs in image generation, an enhanced GAN for image generation is proposed. To improve the quality of generating images, an enhanced generation network is conducted. Deep networks rely on a deep network architecture to extract more structural information [34]. To quickly extract key information, a spatial attention mechanism is proposed [30]. It can use different dimensional channels to extract salient information [30]. Inspired by that, a spatial attention mechanism is fused into the third EResidual ConvBlock from a generation network to extract salient information to improve effects in image generation, where its information can be shown in Section 3.4 Its effectiveness is given in Table 1. That is, a combination of PGGAN and Spatial attention mechanism has obtained a lower FID than that of PGGAN in Table 1. Although deep networks can extract more accurate information to pursue better performance in vision tasks, they may ignore the importance of hierarchical information to limit their better performance and robustness [34]. To overcome the drawbacks, a parallel residual learning operations are set in the third EResidual ConvBlock as shown in Fig. 1 to extract more structural information from different layers. Its competitive results can be proved by comparing ‘A combination of PGGAN, Spatial attention and Parallel residual learning operations’ and ‘A combination of PGGAN and Spatial attention in Table 1. A mixed loss function to update parameters of a GAN to balance speed and accuracy in image generation. Non-saturation loss can make a generator more stable in training process. R1 regularization loss can make a discriminator easier to converge via penalizing gradients of real images to obtain more reliable images. R2 regularization loss can penalty gradients of generating images to easier converge for image generation. Effects of R1 for EIGGAN for image generation can be tested by using ‘A combination of PGGAN, Spatial attention, Parallel residual learning operations, Non-saturation and R1’ and ‘A combination of PGGAN, Spatial attention and Parallel residual learning operations’ in terms of FID in Table 1. It has an improvement of 2.76 in terms of FID in Table 1, which shows effectiveness of R1 for image generation. Positive effects of a mixed loss can verified by comparing ‘A combination of PGGAN, Spatial attention, Parallel residual learning operations, Non-saturation and R1’ and ‘A combination of PGGAN, Spatial attention, Parallel residual learning operations and Mixed loss’ in Table 1. Effectiveness of proposed key techniques can be verified by comparing ‘A combination of PGGAN, Spatial attention, Parallel residual learning operations and Mixed loss’ and ‘PGGAN’ in Table 1.

4.4 Experimental Results

To test the effectiveness of our method, quantitative and qualitative analysis are used to conduct. Quantitative analysis that uses a Deep Convolution GAN (DCGAN) [35], WGAN-GP [36], PGGAN [26], NCSN [37] as comparative methods on CIFAR-10 and CelebA to test performance of the proposed EIGGAN in image generation. We have chosen six indicators, i.e., Frechet Inception Distance (FID) [11], Learned Perceptual Image Patch Similarity (LPIPS) [12], Multi-Scale Structural Similarity Index Measure (MS-SSIM) [13], Kernel Inception Distance (KID) [14], Number of statistically-Different Bins (NDB) [15] and Inception Score (IS) [16] to demonstrate the superiority of our method. All formulas of FID [11], LPIPS [12], MS-SSIM [13], KID [14] and NDB [15] can be given at https://github.com/hellloxiaotian/EIGGAN/blob/main/equation (accessed on 19/03/2024).

As shown in Table 2, we can see that the proposed EIGGAN has obtained the best results in terms of FID, LPIPS, MS-SSIM and KID on CIFAR-10. Also, it has obtained the second result in terms of NDB on CIFAR-10 in Table 2. To verify its robustness, we conduct some extended experiments on CelebA dataset. That is, our EIGGAN has obtained the best performance in terms of FID and LPIPS on CelebA in Table 3. Also, it has obtained the second results in terms of MS-SSIM, KID and NDB in Table 3. According to mentioned illustrations, we can see that the proposed EIGGAN is effective for image generation.

To verify the superiority of our EIGGAN for image generation, we choose newest image generation methods, i.e., StyleGAN2 [38], TransGAN [39], ViTGAN [40], D2WMGAN [41], PFGAN [42] on CIFAR-10 in terms of Information System (IS) to conduct experiments. As mentioned earlier, the FID value is used to evaluate the quality of generated images. In addition, since the CIFAR-10 dataset contains 10 different types of object images, we also tested the IS value to evaluate the type diversity of generated images. To fairly compare the performance of our proposed method for image generation, we conduct some experiments on CIFAR-10. Due to some methods, i.e., StyleGAN2, TransGAN, ViTGAN, D2WMGAN and PFGAN didn’t release codes, public index, i.e., FID and IS from related GANs [38–42] can be obtained. As shown in Table 4, we can see that StyleGAN2 is superior to our EIGGAN. Also, our method has fewer parameters. Also, our method has obtained better effects than that of other methods for image generation in Table 5. In summary, our EIGGAN is comparative for image generation.

Qualitative analysis is composed of two parts: visual generation images and contrastive visual generation images. The first part contains two parts, i.e., ten objects (regarded as planes, cars, birds, cats, deer, dogs, frogs, horses, ships and trucks) and different face images. Also, each object is generated from the CIFAR-10 and each object has eight images with different directions in Fig. 2. Different face images from the CelebA are generated in Fig. 3. These show that our EIGGAN is effective in visual images in image generation.

Figure 2: Generated images on the CIFAR-10 from our EIGGAN

Figure 3: Generated face images from our EIGGAN

The second part conducted some comparative visual images of popular methods and our method for image generation to test the generation ability of our EIGGAN. As shown in Fig. 4, we can see that our EIGGAN is clearer than other methods. As listed in Fig. 5, we can see that our EIGGAN has more detailed information than that of other methods, i.e., DCGAN, WGAN-GP, PGGAN and NCSN. For instance, DCGAN may cause distorted faces. WGGAN-GP may generate blurred faces. NCSN may generate images of poor colour and luster. According to mentioned illustrations, our method is useful for image generation in terms of qualitative and quantitative analysis.

Figure 4: Generated images of different methods on CIFAR-10

Figure 5: Generated images of different methods on CelebA

5  Conclusion

In this paper, we improve a generator to enhance GAN for image generation. To enrich the effect of a generator, spatial attention is applied to a generation network to extract salient information, generating more information that is detailed. To enhance the relation of context, parallel residual operations are used to increase more structural information from different layers in image generation. Taking into consideration the speed and accuracy, a mixed loss function is merged into the generation network to produce images that are more realistic. Overall, the proposed method (EIGGAN) has obtained good performance in image generation. As part of our future work, we will improve the performance of image generation according to the image attributes.

Acknowledgement: This work was supported in part by the Science and Technology Development Fund, in part by Fundamental Research Funds for the Central Universities.

Funding Statement: This work was supported in part by the Science and Technology Development Fund, Macao S.A.R (FDCT) 0028/2023/RIA1, in part by Leading Talents in Gusu Innovation and Entrepreneurship Grant ZXL2023170, in part by the TCL Science and Technology Innovation Fund under Grant D5140240118, in part by the Guangdong Basic and Applied Basic Research Foundation under Grant 2021A1515110079.

Author Contributions: The first author Chunwei Tian gives the main conception and writes of this paper. The second author Haoyang Gao conducts experiments, visual figures and writes part of this paper. The third author Pengwei Wang conducts part experiments. The fourth author Bob Zhang gives key comments. All authors reviewed the results and approved the final version of the manuscript.

Availability of Data and Materials: The datasets used during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.

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