Edge Detection in Color Images Using SVM-SSO Integration

By Muhammad OsamaReviewed by Susha Cheriyedath, M.Sc.May 1 2024

In a recent article published in the journal Scientific Reports, researchers from China proposed a novel method for edge detection in color images using a combination of support vector machine (SVM) and social spider optimization (SSO) algorithms.

Background

Edge detection is a fundamental task in image processing that aims to identify the boundaries of objects or regions in an image. It can be used for various applications such as object recognition, image segmentation, image editing, and medical image analysis. However, performing edge detection in color images is more challenging than in grayscale images due to the complexity of color information across different color channels.

SVM is a machine learning technique that can be used for classification and regression problems. It tries to find a hyperplane that separates the data points of different classes with the maximum margin. It can handle nonlinear problems by using kernel functions that map the data points to a higher-dimensional feature space. However, It requires careful tuning of its hyperparameters, such as the kernel function, the regularization parameter, and the class imbalance parameter, to achieve optimal performance.

SSO is a bio-inspired optimization algorithm that mimics the cooperative behavior of social spiders in a colony. SSO uses two types of search agents, male and female spiders, that have different behaviors and roles. SSO can efficiently explore the search space and find the global optimum by using vibration signals, mating and survival operators, and dominance and non-dominance mechanisms.

About the Research

In the present paper, the authors introduced a two-stage approach for edge detection employing SVM and SSO. In the first stage, the color image undergoes conversion to grayscale, followed by initial edge estimation. This step utilizes an SVM model with a radial basis function (RBF) kernel, with the model's hyperparameters optimized using the SSO algorithm. Pixel intensity and neighboring pixel values serve as features for the SVM model, while the ground-truth edge image acts as the target label.

The objective function for the SSO algorithm is defined as the validation error of the SVM model assessed on a separate set of images. This formulation enables the SSO algorithm to iteratively adjust the SVM's hyperparameters to minimize the discrepancy between predicted and actual edge locations, optimizing the model's performance for detecting edges in color images.

In the second stage, the study improves the initial image edges through a comparison with pairwise combinations of different color layers, aiming to minimize the difference between edge pixels and identify boundaries across different layer combinations. This refinement process is facilitated by the SSO algorithm, which employs a distinct encoding scheme and objective function tailored for this stage.

Each edge pixel is encoded as an optimization variable capable of shifting by a maximum of one pixel in any direction. The objective function is defined as the reciprocal of the mean standard deviation of the edge pixels within the combined color layers. Leveraging a red-green-blue (RGB) color system, the study constructs three matrices: L1, L2, and L3, representing the combinations of RG, GB, and BR layers, respectively.

Furthermore, the study evaluates the performance of the proposed method on various color images sourced from the Berkeley Segmentation Dataset 500 (BSDS500). It compares the method against existing techniques such as Canny, Prewitt, Sobel, and deep learning-based methods.

Additionally, various metrics including precision, recall, F-measure, structural similarity (SSIM), peak signal-to-noise ratio (PSNR) and mean squared error (MSE) are employed to measure the quality of the edge-detected images. This comprehensive evaluation across diverse metrics aims to demonstrate the efficacy of the proposed method in comparison to established edge detection methodologies.

Research Findings

The outcomes indicated that the developed method outperformed the existing methods in terms of accuracy and quality of edge detection tasks. Specifically, the novel method demonstrated higher accuracy in identifying image edges, with an accuracy of 93.11% for the utilized database. This represents an improvement of 0.74% compared to other approaches.

Additionally, the proposed method was shown to produce edge-detected images with higher structural similarity, lower noise, and lower error when compared to existing methods. These results underscored the effectiveness of the proposed approach in accurately detecting edges in color images.

The authors demonstrated the applicability of the new method in various domains requiring edge detection in color images, such as object detection and identification of lesion regions in medical images. They showcased examples of edge detection in color images of natural scenes, fruits, flowers, animals, and human faces.

In addition, examples of edge detection in color medical images, including retinal images, skin images, and brain images, were presented. Moreover, the study claimed that the proposed method could enhance the performance of these applications by providing more accurate and consistent edge boundaries in color images.

Conclusion

In summary, the novel approach proved to be simple and effective in detecting edges in color images. It successfully addressed limitations observed in existing methods, including high computational complexity, low accuracy, and sensitivity to noise.

Moving forward, the researchers acknowledged the limitations and challenges and proposed directions for future work. They recommended exploring alternative color spaces, kernel functions, and optimization algorithms to enhance the proposed approach further. Additionally, they suggested extending the method to other image-processing tasks, such as image segmentation, enhancement, and compression.