Arbitrary style transfer (AST), a popular AI-powered photo editing function, aims to strike an optimal balance between content and style injection from two images in order to generate a novel high-fidelity stylised image. Recently, diffusion models have been applied to AST due to their high generation quality as well as flexibility to embed conditions. However, these models are still not satisfactory and may exhibit inferior performance compared to non-diffusion based methods. This is due to the diffusion process not being purposely designed for AST, leading to suboptimal solutions to trade-off content preservation and style embedding. In this paper, we propose ACID-Style, a novel adaptive condition injection diffusion-based AST framework for improved content/style feature injection to address this research challenge. Using two lightweight adapters, a content and a style injection module, and an adaptive injection mechanism, our approach is able to fully exploit a pre-trained stable diffusion model for AST-specific adaptation and our diffusion model thus learns the most effective timing for content and style injection in the diffusion sampling process. Comprehensive evaluations demonstrate that our method achieves superior style transfer performance, both quantitatively and qualitatively, compared to other state-of-the-art style transfer methods.

Weakly supervised semantic segmentation (WSSS) aims to provide accurate pixel-level annotation based on only weak guidance, primarily derived from image-level labels. Recent WSSS methods exploit pseudo-labels generated from improved class activation maps (CAMs) to train a fine-grained classification model for semantic segmentation. However, these pseudo-labels are unreliable because they tend to either miss parts of the objects or include irrelevant regions due to weak guidance from individual images. In this paper, we propose a simple yet effective iterative mix-up strategy, Pseudo-Label-based Mix (PL-Mix), that refines pseudo-labels iteratively, thereby further enhancing WSSS performance. During each iteration, we migrate object regions from pseudo-labels produced in previous steps and render them with new contexts in a mix-up fashion. Due to model consistency enforcement across varied backgrounds and new combinations of multiple objects from enriched image samples, these pseudo-labels progressively become more accurate and reliable. Further enhanced by a masking strategy and a CAM-based earth mover’s distance loss, we achieve state-of-the-art performance on the PASCAL VOC2012 and MS COCO2014 benchmark datasets.

Image Steganography without Embedding (SWE) is an emerging data hiding paradigm. Instead of embedding a secret message into a container image, SWE synthesises a novel image by using the secret message as a latent code. Current SWE methods have achieved high synthesis quality and strong resistance to steganalysis tools. However, it remains challenging to apply the SWE due to two reasons: (i) lack of synthesis diversity and (ii) recovery of secret messages under malicious image attacks. In this paper, we present a novel SWE framework with a disentanglement autoencoder to tackle the above challenges. Specifically, the autoencoder disentangles an image into a structure and texture representation. Then, we exploit the stability of the structure representation to improve secret message recovery reliability, while increasing synthesis diversity by randomising texture representations and employing a chaotic system for structure randomisation to enhance its security. To further achieve a robust message recovery under malicious attacks, an adversarial learning strategy is introduced into our framework, which guarantees high recovery accuracy. Our method outperforms other state-of-the-art SWE methods in terms of synthesis quality, synthesis diversity and secret message recovery accuracy under various image attacks. The source code is publicly available athttps://github.com/Lemok00/RDI-SWE.

Current high-capacity image steganography methods face challenges in balancing hidden capacity, imperceptibility, and recovery quality. Existing embedding-based image-in-image steganography approaches tend to produce detectable artifacts when hiding multiple images, whereas existing generative methods struggle to conceal full-sized secret images and often generate unrealistic stego images. To address these issues, this paper proposes a novel generative steganography approach that hides multiple secret images in a single realistic generated image. Our main contributions include a meticulously designed autoencoder that compresses and injects secret images into the shallow layer of the generator to increase hidden capacity, a three-stage optimization strategy for stable training to enhance the recovery quality of secret images, and an automatic image selection procedure which explores the advantage of generation diversity to enhance the imperceptibility of stego images. Experimental results demonstrate that our method outperforms embedding-based approaches by achieving higher recovered image quality with a PSNR value of 30.45 dB when concealing four images while maintaining stronger resistance against steganalysis tools, with an accuracy of 50%. Against generative approaches, our method achieves a higher hidden capacity while preserving a superior visual quality of stego images, with a FID of 6.97, surpassing the suboptimal method's FID of 22.72.

Unauthorised face recognition (FR) systems have posed significant threats to digital identity and privacy protection. To alleviate the risk of compromised identities, recent makeup transfer-based attack methods embed adversarial signals in order to confuse unauthorised FR systems. However, their major weakness is that they set up a fixed image unrelated to both the protected and the makeup reference images as the confusion identity, which in turn has a negative impact on both attack success rate and visual quality of transferred photos. In addition, the generated images cannot be recognised by authorised FR systems once attacks are triggered. To address these challenges, in this paper, we propose a Recoverable Makeup Transferred Generative Adversarial Network (RMT-GAN) which has the distinctive feature of improving its image-transfer quality by selecting a suitable transfer reference photo as the target identity. Moreover, our method offers a solution to recover the protected photos to their original counterparts that can be recognised by authorised systems. Experimental results demonstrate that our method provides significantly improved attack success rates while maintaining higher visual quality compared to state-of-the-art makeup transfer-based adversarial attack methods. Our code and supplementary materials are available on Github.

Recently, numerous robust image hashing schemes have been developed for content identification. However, many of these schemes face the challenges of maintaining discrimination while simultaneously resisting large-scale attacks. In this paper, we propose a robust image hashing scheme based on Contrastive Masked Autoencoder with weak-strong augmentation Alignment (CMAA). Leveraging contrastive learning, CMAA is designed to learn features that are robust to large-scale and hybrid attacks while maintaining the discrimination of those features. Specifically, it utilizes distribution divergence to align weak attack augmented features with strong attack augmented features, namely weak-strong augmentation alignment, to enhance the robustness to strong attacks. In addition, a masked vision transformer is incorporated to further enhance content identification performance. CMAA also includes a parameter-free quantization layer to mitigate the loss induced by binarization. Experimental results demonstrate that our method exhibits remarkable robustness against various attacks, including challenging ones such as rotation and hybrid attacks, and delivers excellent identification performance with a F1 score close to 1.0. Our code and supplementary materials are available on Github.

In collaborative system, a large amount of digital image transmission requires a reliable content identification system to ensure the authenticity and copyright of these images. Robust image hashing schemes could efficiently extract robust features of images without manipulating the original image, making them an effective solution for content identification. However, existing schemes face the challenge of resisting complex attacks, such as diverse attack types and their sophisticated combinations, in the real world while maintaining discrimination. The complexity of attacks is reflected in the diversity of attack types, the variation in attack intensity and the combination of multiple attacks. In this study, we propose a robust image hashing approach based on Mixture-of-experts with Hard-sample mining contrastive learning (MiHa). In particular, MiHa utilizes a mixture-of-experts architecture to adaptively extract features from the image under various attacks, including hybrid attacks, thereby enhancing the robustness. Additionally, large-scale attacks can generate hard samples for contrastive learning. To address this, we propose a hard-sample mining contrastive loss that assigns greater weight to these hard samples, thereby further improving the performance of MiHa. Extensive experiments demonstrate that our method achieves superior robustness against various attacks while maintaining competitive discrimination.

Retrieval-augmented generation (RAG) enables large language models (LLMs) to answer questions without hallucinations by retrieving external knowledge. However, it still struggles with addressing global and reasoning-intensive questions. The recently proposed GraphRAG tackles these issues by organizing the knowledge base into hierarchical graph communities, but its retrieval mechanism results in high computational costs and overly generalized answers. To overcome these limitations, we propose a novel community embedding-based GraphRAG framework comprising three key components: a graph community encoder that embeds community descriptions into dense vectors for efficient knowledge graph retrieval, a hierarchical retriever that leverages the communities’ hierarchy to balance abstract and specific information, and an iterative question processor that recursively decomposes a multi-hop question to enable multi-step reasoning. Experiments demonstrate that our method reduces token consumption by 96.7% compared to GraphRAG while achieving comparable performance, and it outperforms other state-of-the-art RAG approaches in terms of answer quality.

Copyright protection of depth image-based rendering (DIBR) videos has raised significant concerns due to their increasing popularity. Zero-watermarking, emerging as a powerful tool to protect the copyright of DIBR 3D videos, mainly relies on traditional feature extraction methods, thus necessitating improvements in robustness against complex geometric attacks and its ability to strike a balance between robustness and distinguishability. This paper presents a novel zero-watermarking scheme based on cross-modality feature fusion within a contrastive learning framework. Our approach integrates complementary information from 2D frames and depth maps using a cross-modality attention feature fusion mechanism to obtain discriminative features. Moreover, our features achieve a better trade-off between robustness and distinguishability by leveraging a designed contrastive learning strategy with an adversarial distortion simulator. Experimental results demonstrate our remarkable performance by reducing the false negative rates to around 0.2% when the false positive rate is equal to 0.5%, which is superior to the state-of-the-art zero-watermarking methods. • Use contrastive learning to balance watermarking robustness and distinguishability. • Employ an adversarial distortion simulator to enhance robustness against various attacks. • Design cross-modality fusion mechanism to achieve better feature representation.

Video instance segmentation (VIS) is an evolving research topic in computer vision that aims to simultaneously detect, segment, and track semantic objects across multiple video frames. However, existing VIS methods are typically unaware of the reliability of the training samples from insufficient and imbalanced datasets, leading to suboptimal performance. To address this challenge, we propose a memory-based conditional neural process (MemCNP) module to exploit the strengths of both memory networks and the CNP model which handles heterogeneous latent space distributions for reliable modelling with insufficient data. Our MemCNP utilises predicted uncertainty to regularise VIS predictions as well as to identify reliable samples for effective training. Notably, our MemCNP is model-agnostic and can thus be seamlessly integrated into various VIS models to improve their performance. Extensive experiments on the YouTube-VIS and OVIS datasets demonstrate the effectiveness of MemCNP regardless of the underlying model architecture. • A memory-based conditional neural process. • Reliability modelling for object detection. • Uncertainty-based dynamic training sample selection. • Contrastive instance tracking.

Zero-watermarking is an emerging distortion-free copyright protection method for volumetric medical images. However, achieving both robustness against various malicious attacks and distinguishability between individual images remains challenging. In this article, we propose a novel attack-defending contrastive learning zero-watermarking (ADCL-ZW) scheme to tackle the above challenge using deep learning-based representations. In our approach, we design an attack-defending data enrichment mechanism to enhance the watermarking robustness by generating a large number of image samples under various watermarking attacks. Subsequently, features for both watermarking distinguishability and robustness are enhanced through application of a contrastive loss. In particular, we implement a dual-stream Siamese network architecture to effectively handle both signal attacks and geometric attacks in order to enhance the watermarking performance. Experimental results demonstrate that ADCL-ZW achieves stronger watermarking robustness and a better tradeoff between watermarking robustness and distinguishability compared with state-of-the art zero-watermarking methods. One of the highlighted metrics is that the false-negative rate of ADCL-ZW achieves 0.01 when a fixed false-positive rate is set to 1%, which is more than 13.3 times better than the benchmark methods.

Micro-expressions (MEs) are subtle and brief facial expressions that occur involuntarily and may reveal hidden emotions. Due to MEs' weak intensities, it is challenging to discriminate MEs from image noise through AU detection results or spatio-temporal features. To model authentic ME patterns rather than overfitting to noise, we propose a novel multiframe strategy that captures detailed motion patterns and a two-layered feature encoding scheme to model interactions across different parts of the feature maps. Furthermore, we propose a novel facial Action Unit Graph Convolutional Network (AU GCN) that can adapt to testing input data through an AU detection module and a learnable adjacent matrix with a transformer encoder. Finally, we fuse the enhanced spatiotemporal features and AU GCN results to recognize MEs. Experimental results show that our methods outperform SOTA in F1 scores on SAMM and CASME II datasets, and also achieves the highest accuracy on CASME II dataset.

Face forgery detection has recently progressed to address the threat from image synthesis technology, although robust face forgery detection under heterogeneous attacks remains challenging. When forgers leverage image post-processing techniques to manipulate forged photos, recent detection methods exhibit significant performance degradation. In this work, we propose a novel multi-strategy adversarial learning (MAL) method to extract salient features in order to achieve more reliable forgery detection under attacks. In particular, our MAL framework creates a large number of positive and negative sample pairs by designing a composite attack generation module with supervised contrastive training to ensure the attack robustness. In addition, we exploit two intuitive strategies, hard sample selection and region consistency, to enhance the contrastive losses for further strengthened feature reliability. Extensive experimental results demonstrate our proposed method to outperform recent state-of-the-art face forgery detection methods in terms of overall accuracy under various single and composite attacks.

The facial expression spotting task serves as the foundation for expression recognition, focusing on identifying the onset and offset frames of facial expressions. State-of-the-art methods usually rely on detecting if optical flow intensity within facial feature regions exceeds a threshold. However, facial expressions may not recover to neutral at the offset frame, leading to sustained high optical flow intensities. Additionally, non-expression motion may also cause high optical flow intensities. Both scenarios have the potential to result in false positives during spotting. To address these issues, this paper introduces a two-stage spotting strategy and a spectrum-based post-processing method. Experimental results demonstrate the effectiveness of our approach in reducing false positives caused by the two issues. Finally, we evaluated our method on MEGC2022-TestSet and achieved an overall F1 score of 0.3776, surpasses the state-of-the-art methods.

Adversarial attack has posed a significant threat to modern deep learning based models. Recently, various adversarial defending algorithms are proposed to tackle the problem. Among them, diffusion-based adversarial purification approaches offer the most promising solutions. However, their effectiveness are limited due to the strong adversarial perturbations presented in attacked images. These adversarial signals hinder the introduction of guidance into diffusion models in order to improve the defence efficacy. In this paper, we propose a novel approach to embed reliable guidance into diffusion-based adversarial purification model to improve both its defence effectiveness and efficiency. In specific, we present a diffusion sampling guidance enhanced by a pretrained denoising network as a prior constraint to improve the adversarial defence performance. Experimental results convincingly demonstrate the superior performance of the proposed approach in terms of enhanced robustness to standard image classifiers when compared to state-of-the-art adversarial defence approaches.

Federated learning (FL) allows multiple participants to collaboratively build deep learning (DL) models without directly sharing data. Consequently, the issue of copyright protection in FL becomes important since unreliable participants may gain access to the jointly trained model. Application of homomorphic encryption (HE) in a secure FL framework prevents the central server from accessing plaintext models. Thus, it is no longer feasible to embed the watermark at the central server using existing watermarking schemes. In this article, we propose a novel client-side FL watermarking scheme to tackle the copyright protection issue in secure FL with HE. To the best of our knowledge, it is the first scheme to embed the watermark to models under a secure FL environment. We design a black-box watermarking scheme based on client-side backdooring to embed a pre-designed trigger set into an FL model by a gradient-enhanced embedding method. Additionally, we propose a trigger set construction mechanism to ensure that the watermark cannot be forged. Experimental results demonstrate that our proposed scheme delivers outstanding protection performance and robustness against various watermark removal attacks and ambiguity attack.

Class activation maps (CAMs) have emerged as a popular technique to improve model interpretability of deep learning-based models. While existing CAM methods are able to extract salient semantic regions to provide high-confidence pseudo-labels for downstream tasks such as semantic segmentation, they are less effective when dealing with multi-object scenes. In this paper, we design a multi-channel weight assignment scheme that learns from both positive and negative regions to yield an improved CAM model for images comprising multiple objects. We demonstrate the effectiveness of our proposed method on two new data sets, a cat-and-dog dataset and a PASCAL VOC 2012-based multi-object dataset, and show it to compare favourably with other state-of-the-art CAM methods, outperforming them in terms of both mIoU and inter-object activation ratio (IAR), a new evaluation measure proposed to evaluate CAM performance in multi-object scenes.

Synthesis-based steganography without embedding (SWE) methods transform secret messages to container images synthesised by generative networks, which eliminates distortions of container images and thus can fundamentally resist typical steganalysis tools. However, existing methods suffer from weak message recovery robustness, synthesis fidelity, and the risk of message leakage. To address these problems, we propose a novel robust steganography without embedding method in this paper. In particular, we design a secure weight modulation-based generator by introducing secure factors to hide secret messages in synthesised container images. In this manner, the synthesised results are modulated by secure factors and thus the secret messages are inaccessible when using fake factors, thus reducing the risk of message leakage. Furthermore, we design a difference predictor via the reconstruction of tampered container images together with an adversarial training strategy to iteratively update the estimation of hidden messages. This ensures robustness of recovering hidden messages, while degradation of synthesis fidelity is reduced since the generator is not included in the adversarial training. Extensive experimental results convincingly demonstrate that our proposed method is effective in avoiding message leakage and superior to other existing methods in terms of recovery robustness and synthesis fidelity.

Abstract Face swapping is a technique that replaces a face in a target media with another face of a different identity from a source face image. Currently, research on the effective utilisation of prior knowledge and semantic guidance for photo‐realistic face swapping remains limited, despite the impressive synthesis quality achieved by recent generative models. In this paper, we propose a novel conditional Denoising Diffusion Probabilistic Model (DDPM) enforced by a two‐level face prior guidance. Specifically, it includes (i) an image‐level condition generated by a 3D Morphable Model (3DMM), and (ii) a high‐semantic level guidance driven by information extracted from several pre‐trained attribute classifiers, for high‐quality face image synthesis. Although swapped face image from 3DMM does not achieve photo‐realistic quality on its own, it provides a strong image‐level prior, in parallel with high‐level face semantics, to guide the DDPM for high fidelity image generation. The experimental results demonstrate that our method outperforms state‐of‐the‐art face swapping methods on benchmark datasets in terms of its synthesis quality, and capability to preserve the target face attributes and swap the source face identity.

Weakly supervised semantic segmentation (WSSS) has gained significant popularity as it relies only on weak labels such as image level annotations rather than the pixel level annotations required by supervised semantic segmentation (SSS) methods. Despite drastically reduced annotation costs, typical feature representations learned from WSSS are only representative of some salient parts of objects and less reliable compared to SSS due to the weak guidance during training. In this paper, we propose a novel Multi-Strategy Contrastive Learning (MuSCLe) framework to obtain enhanced feature representations and improve WSSS performance by exploiting similarity and dissimilarity of contrastive sample pairs at image, region, pixel and object boundary levels. Extensive experiments demonstrate the effectiveness of our method and show that MuSCLe outperforms current state-of-the-art methods on the widely used PASCAL VOC 2012 dataset.

Conventional steganography approaches embed a secret message into a carrier for concealed communication but are prone to attack by recent advanced steganalysis tools. In this paper, we propose Image DisEntanglement Autoencoder for Steganography (IDEAS) as a novel steganography without embedding (SWE) technique. Instead of directly embedding the secret message into a carrier image, our approach hides it by transforming it into a synthesised image, and is thus fundamentally immune to typical steganalysis attacks. By disentangling an image into two representations for structure and texture, we exploit the stability of structure representation to improve secret message extraction while increasing synthesis diversity via randomising texture representations to enhance steganography security. In addition, we design an adaptive mapping mechanism to further enhance the diversity of synthesised images when ensuring different required extraction levels. Experimental results convincingly demonstrate IDEAS to achieve superior performance in terms of enhanced security, reliable secret message extraction and flexible adaptation for different extraction levels, compared to state-of-the-art SWE methods.

Zero-watermarking is a key technique for achieving lossless and flexible copyright protection of depth image-based rendering (DIBR) videos. Existing approaches extract features of both 2D frames and depth maps via a single mechanism to protect them simultaneously. However, it is difficult for these schemes to fully satisfy the copyright protection requirements of the two components, including the remarkable discriminative capability of 3D videos and robustness against various attacks. Hence, in this paper, we propose a novel multiple-feature-based zero-watermarking scheme to protect the copyright of DIBR 3D videos. To the best of our knowledge, this is the first scheme that integrates multiple features to improve both the discriminative capability and robustness against various attacks. Specifically, dual-tree complex wavelet transform and discrete cosine transform features enhance the robustness against DIBR conversion and noise addition, respectively, while ring-partition statistical residual features ensure robustness against geometric attacks and provide sufficient discriminative capacity. In addition, we use a logistic-logistic chaotic system to encrypt these multiple features for enhanced security and design an attention-based fusion approach to offer an optimal copyright protection solution. Extensive experimental results demonstrate that our proposed scheme has stronger robustness and discriminative capacity compared to state-of-the-art zero-watermarking methods.

Interest in image hiding has been continually growing. Recently, deep learning-based image hiding approaches improve the hidden capacity significantly. However, the major challenges of the existing methods are that they are difficult to balance between the errors of the modified cover image and those of the recovered secret image. To solve this problem, in this paper, we develop an image hiding algorithm based on a joint compressive autoencoder framework. Further, we propose a novel strategy to enlarge the hidden capacity, i.e., hiding multi-images in one container image. Specifically, our approach provides an extremely high image hidden capacity coupled with small reconstruction errors of the secret image. More importantly, we tackle the trade-off problem of earlier approaches by mapping the image representations in the latent spaces of the joint compressive autoencoder models, leading to both high visual quality of the container image and low reconstruction error the secret image. In an extensive set of experiments, we confirm our proposed approach to outperform several state-of-the-art image hiding methods, yielding high imperceptibility and steganalysis resistance of the container images with high recovery quality of the secret images, while improving the image hidden capacity significantly (four times higher than full-image hiding capacity).

Copyright protection of depth image-based rendering (DIBR) 3D videos is crucial due to the popularity of these videos. Despite the success of recent watermarking schemes, it is still challenging to ensure the robustness against strong geometric attacks when both lossless quality and distinguishability of protected videos are required. In this paper, we pro-pose a novel zero-watermarking scheme to improve the performance under strong geometric attacks when satisfying the other two requirements. In our scheme, CT-SVD-based features are extracted to ensure both distinguishability and robustness against signal processing and DIBR conversion at-tacks, while a SIFT-based rectication mechanism is designed to resist geometric attacks. Further, an attention-based fusion strategy is proposed to complement the robustness of rectied and unrectied CT-SVD features. Experimental results demonstrate that our scheme outperforms the existing zero-watermarking schemes in terms of distinguishability and robustness against strong geometric attacks such as rotation, cyclic translation and shearing.

In recent years, coverless image steganography attracts significant attentions due to its distortion-free trait on carrier images to avoid the detection by steganalysis tools. Despite this advantage, current coverless methods face several challenges, e.g., vulnerability to geometrical attacks and low hidden capacity. In this paper, we propose a novel coverless steganography algorithm based on chaotic encrypted dual radial harmonic Fourier moments (DRHFM) to tackle the challenges. In specific, we build mappings between the extracted DRHFM features and secret messages. These features are robust to various of attacks, especially to geometrical attacks. We further deploy the DRHFM parameters to adjust the feature length, thus ensuring the high hidden capacity. Moreover, we introduce a chaos encryption algorithm to enhance the security of the mapping features. The experimental results demonstrate that our proposed scheme outperforms the state-of-the-art coverless steganography based on image mapping in terms of robustness and hidden capacity.

This paper proposes a novel information hiding method designed for H.266/Versatile Video Coding (VVC) compressed video streams. In this work, we explore two exclusive tools in H.266/VVC standard, named Multiple Transform Selection (MTS) and Cross-component linear model (CCLM), to hide information. These two tools are utilized to preserve high video reconstruction quality and compression efficiency as well as enhance hidden capacity. In specific, MTS is for hiding information into luminance blocks by modifying the selections of transforms. Comparing with other tools, MTS has less significant impact on compression quality and efficiency. In addition, CCLM is further used to hide information into chrominance blocks to further enlarge the hidden capacity with little impact on the other two metrics. To our best knowledge, it is the first information hiding method exclusively designed for H.266/VVC. Experimental results show that our proposed information hiding method ensures high hidden capacity, remarkable video reconstruction quality and insignificant impact on compression efficiency, which achieves better overall performances comparing to existing methods for compressed video.

Federated learning (FL) has become an emerging distributed framework to build deep learning models with collaborative efforts from multiple participants. Consequently, copyright protection of FL deep model is urgently required because too many participants have access to the joint-trained model. Recently, Secure FL framework is developed to address data leakage issue when central node is not fully trustable. This encryption process has made existing DL model watermarking schemes impossible to embed watermark at the central node. In this paper, we propose a novel client-side Federated Learning watermarking method to tackle the model verification issue under the Secure FL framework. In specific, we design a backdoor-based watermarking scheme to allow model owners to embed their pre-designed noise patterns into the FL deep model. Thus, our method provides reliable copyright protection while ensuring the data privacy because the central node has no access to the encrypted gradient information. The experimental results have demonstrated the efficiency of our method in terms of both FL model performance and watermarking robustness.

Image hiding has received significant attention due to the need of enhanced multimedia services such as multimedia security and meta-information embedding for multimedia augmentation. Recently, deep learning-based methods have been introduced that are capable of significantly increasing the hidden capacity and supporting full-size image hiding. However, these methods suffer from the necessity to balance the errors of the modified cover image and the recovered hidden image. In this paper, we propose a novel joint compressive autoencoder (J-CAE) framework to design an image hiding algorithm that achieves full-size image hidden capacity with small reconstruction errors of the hidden image. More importantly, our approach addresses the trade-off problem of previous deep learning-based methods by mapping the image representations in the latent spaces of the joint CAE models. Thus, both visual quality of the container image and recovery quality of the hidden image can be simultaneously improved. Extensive experimental results demonstrate that our proposed method outperforms several state-of-the-art deep learning-based image hiding techniques in terms of imperceptibility and recovery quality of the hidden images while maintaining full-size image hidden capacity.

Image hiding, one of the most important data hiding techniques, is widely used to enhance cybersecurity when transmitting multimedia data. In recent years, deep learning-based image hiding algorithms have been designed to improve the embedding capacity whilst maintaining sufficient imperceptibility to malicious eavesdroppers. These methods can hide a full-size secret image into a cover image, thus allowing full-image-to-image hiding. However, these methods suffer from a trade-off challenge to balance the possibility of detection from the container image against the recovery quality of secret image. In this paper, we propose Camouflage Generative Adversarial Network (Cam-GAN), a novel two-stage coverless full-image-to-image hiding method named, to tackle this problem. Our method offers a hiding solution through image synthesis to avoid using a modified cover image as the image hiding container and thus enhancing both image hiding imperceptibility and recovery quality of secret images. Our experimental results demonstrate that Cam-GAN outperforms state-of-the-art full-image-to-image hiding algorithms on both aspects.

Colour quantisation is a common image processing technique to reduce the number of distinct colours in an image which are then represented by a colour palette. Selection of appropriate entries in this palette is challenging since the quality of the quantised image is directly dictated by the palette colours. In this paper, we propose a novel colour quantisation algorithm based on the human mental search (HMS) algorithm and subsequent refinement of the colour palette using k-means. HMS is a recent population-based metaheuristic algorithm that has been shown to yield good performance on a variety of optimisation problems. In the first stage, we use HMS to find a high-quality initial colour palette. In the second stage, this palette is refined using k-means to converge towards a local optimum and thus to further improve the quality of the quantised image. We evaluate our algorithm on a set of benchmark images and compare it to several conventional and soft computing-based colour quantisation algorithms to demonstrate excellent image quality, outperforming the other methods.

Micro-expression (ME) recognition is an effective method to detect lies and other subtle human emotions. Machine learning-based and deep learning-based models have achieved remarkable results recently. However, these models are vulnerable to overfitting issue due to the scarcity of ME video clips. These videos are much harder to collect and annotate than normal expression video clips, thus limiting the recognition performance improvement. To address this issue, we propose a micro-expression video clip synthesis method based on spatial-temporal statistical and motion intensity evaluation in this paper. In our proposed scheme, we establish a micro-expression spatial and temporal statistical model (MSTSM) by analyzing the dynamic characteristics of micro-expressions and deploy this model to provide the rules for micro-expressions video synthesis. In addition, we design a motion intensity evaluation function (MIEF) to ensure that the intensity of facial expression in the synthesized video clips is consistent with those in real -ME. Finally, facial video clips with MEs of new subjects can be generated by deploying the MIEF together with the widely-used 3D facial morphable model and the rules provided by the MSTSM. The experimental results have demonstrated that the accuracy of micro-expression recognition can be effectively improved by adding the synthesized video clips generated by our proposed method.

Glaucoma is a chronic eye disease that leads to irreversible vision loss. The Cup-to-Disc Ratio (CDR) serves as the most important indicator for glaucoma screening and plays a significant role in clinical screening and early diagnosis of glaucoma. In general, obtaining CDR is subjected to measuring on manually or automatically segmented optic disc and cup. Despite great efforts have been devoted, obtaining CDR values automatically with high accuracy and robustness is still a great challenge due to the heavy overlap between optic cup and neuroretinal rim regions. In this paper, a direct CDR estimation method is proposed based on the well-designed semi-supervised learning scheme, in which CDR estimation is formulated as a general regression problem while optic disc/cup segmentation is cancelled. The method directly regresses CDR value based on the feature representation of optic nerve head via deep learning technique while bypassing intermediate segmentation. The scheme is a two-stage cascaded approach comprised of two phases: unsupervised feature representation of fundus image with a convolutional neural networks (MFPPNet) and CDR value regression by random forest regressor. The proposed scheme is validated on the challenging glaucoma dataset Direct-CSU and public ORIGA, and the experimental results demonstrate that our method can achieve a lower average CDR error of 0.0563 and a higher correlation of around 0.726 with measurement before manual segmentation of optic disc/cup by human experts. Our estimated CDR values are also tested for glaucoma screening, which achieves the areas under curve of 0.905 on dataset of 421 fundus images. The experiments show that the proposed method is capable of state-of-the-art CDR estimation and satisfactory glaucoma screening with calculated CDR value.

The segmentation of small blood vessels whose width is less than 2 pixels in retinal images is a challenging problem. Existed methods rarely focus on the differences between small vessels and big vessels when doing segmentation. Therefore, previous methods are not accurate enough on small blood vessel segmentation. To effectively segment small blood vessels in retinal images including big vessels, we proposed a novel multi-label classification scheme for retinal vessel segmentation. In our proposed scheme, a local de-regression model is designed for multi-labeling and a convolutional neural network is used for multi-label classification. At addition, a local regression method is utilized to transform multi-label into binary label for locating small vessels. The experimental results show that our method achieves prominent performance for automatic retinal vessel segmentation, especially for small blood vessels.

Automatic optic disc (OD) localisation and segmentation is still a great challenge in computer‐aided diagnosis and screening system. Here, a new OD segmentation algorithm is proposed based on the distinct features of OD in terms of its intensity and shape. The algorithm includes four stages: image preprocessing, image segmentation, ellipse fitting, and OD localisation and segmentation. In the preprocessing stage, the blood vessel in the input retinal image is removed by using the morphological operation and median filtering in HSL (hue–saturation–lightness) colour space. In the image segmentation and ellipse fitting stages, the fractional‐order Darwinian particle swarm optimisation algorithm is used to extract the brightest region, and the least‐squares optimisation is adopted to detect elliptical OD shape. Finally, the smooth OD borders are generated in the last stage. The proposed method is evaluated by the centroid difference, overlapping ratio, overlap score, and success indexes. Experimental results on the retinal images from DRION, MESSIDOR, ORIGA, and many other public databases demonstrate that the proposed method has superior performance, and may be a suitable tool for automated retinal image analysis.

Contour is a critical feature for image description and object recognition in many computer vision tasks. However, detection of object contour remains a challenging problem because of disturbances from texture edges. This letter proposes a scheme to handle texture edges by implementing contour integration. The proposed scheme integrates structural segments into contours while inhibiting texture edges with the help of the orientation histogram-based center-surround interaction model. In the model, local edges within surroundings exert a modulatory effect on central contour cues based on the co-occurrence statistics of local edges described by the divergence of orientation histograms in the local region. We evaluate the proposed scheme on two well-known challenging boundary detection data sets (RuG and BSDS500). The experiments demonstrate that our scheme achieves a high [Formula: see text]-measure of up to 0.74. Results show that our scheme achieves integrating accurate contour while eliminating most of texture edges, a novel approach to long-range feature analysis.

In this letter, a localization algorithm, which combines Hough transform and Doppler processing, is proposed for Doppler radar human sensing applications. The Hough transform is first applied to extract the interested target components and real-time estimate their instantaneous frequencies (IFs). Then, based on the IF estimation result, the target movement trajectories are synthesized by Doppler processing. To improve the detection accuracy and robustness, a generalized linear model is proposed for Hough transform, which can achieve highly dimensional frequency fitting to compensate the nonlinear error, meanwhile maintaining a low level of computational complexity for real-time processing. Experimental results are presented to illustrate the performance of the proposed algorithm.

3D video provides an immersive experience to viewers and is getting more and more popular. The solution to create 3D video from 2D video is low-cost compared with that captures 3D video directly, and the generation of depth map from 2D video is a key in the 2D-3D video conversion systems. Therefore, protection of depth map is vital for 3D video. In this paper, a digital blind watermarking scheme based on Quantization Index Modulation (QIM) algorithm is proposed in which the copyright information is embedded in the DCT coefficients of depth map imperceptibly. The experimental results show that the proposed scheme has good robustness against video attacks such as salt noise, median filtering, wiener filtering, and scaling. In the meanwhile, the stereo video embedded watermarking can accomplish zero distortion in comparison with the original one.