Wide-angle Visual Feature Matching for Outdoor Localization

얼굴추적은 3차원 공간상에서 머리(head)와 안면(face)의 움직임을 추정하는 기술로, 얼굴 표정 감정인식과 같은 상위 분석단계의 중요한 기반기술이다. 본 논문에서는 AAM 기반의 얼굴추적 알고리즘을 제안한다. AAM은 변형되는 대상을 분할하고 추적하는데 광범위하게 적용되고 있다. 그러나 여전히 여러 가지 해결해야할 제약사항들이 있다. 특히 자체중첩(self-occlusion)과 부분적인 중첩, 그리고 일시적으로 완전히 가려지는 완전중첩 상황에서 보통 국부해에 수렴(local convergence)하거나 발산하기 쉽다. 본 논문에서는 이러한 중첩상황에 대한 AAM의 강인성을 향상시키기 위해서 SIFT 특징을 이용하고 있다. SIFT는 일부 영상의 특징점으로 안정적인 추적이 가능하기 때문에 자체와 부분중첩에 효과적이며, 완전중첩의 상황에도 SIFT의 전역적인 매칭성능으로 별도의 재초기화 없이 연속적인 추적이 가능하다. 또한 추적과정에서 큰 자세변화에 따른 움직임을 효과적으로 추정하기 위해서 다시점(multi-view) 얼굴영상의 SIFT 특징을 온라인으로 등록하여 활용하고 있다. 제안한 알고리즘의 이러한 강인성은 위 세 가지 중첩상황에 대해서 기존 알고리즘들과의 비교실험을 통해서 보여준다. Face tracking is to estimate the motion of a non-rigid face together with a rigid head in 3D, and plays important roles in higher levels such as face/facial expression/emotion recognition. In this paper, we propose an AAM-based face tracking algorithm. AAM has been widely used to segment and track deformable objects, but there are still many difficulties. Particularly, it often tends to diverge or converge into local minima when a target object is self-occluded, partially or completely occluded. To address this problem, we utilize the scale invariant feature transform (SIFT). SIFT is an effective method for self and partial occlusion because it is able to find correspondence between feature points under partial loss. And it enables an AAM to continue to track without re-initialization in complete occlusions thanks to the good performance of global matching. We also register and use the SIFT features extracted from multi-view face images during tracking to effectively track a face across large pose changes. Our proposed algorithm is validated by comparing other algorithms under the above 3 kinds of occlusions.

Iris feature extraction is the crucial stage of the whole iris recognition process. A brief introduction of iris recognition system is made firstly in this paper, then presented the method of iris feature extraction and matching using Scale Invariant Feature Transform (SIFT). Through analyzing iris feature extraction and matching method, we found in conventional iris recognition system, Iris features are not consistent because most feature extraction techniques are sensitive to the variations of captured iris image data, are impacted of natural illumination or other variant conditions easily. So this paper used SIFT feature which is invariant to image scaling and rotation, and partially invariant to change in illumination. They are also well localized in both the spatial and frequency domains. SIFT feature shows a higher feasibility in the iris feature extraction and matching process.

Scale invariant feature transform(SIFT) is an algorithm to extract distinctive and invariant features from images to achieve reliable object matching between different images in variant scales and rotations. However, SIFT's huge computation impedes its real-time implementation. In this paper, a Fast-Gaussian SIFT(FG-SIFT) is proposed. Keypoint detection is optimized in FG-SIFT. SIFT's 2-D difference of Gaussian(DoG) in Gaussian Scale-Space(GSS) is separated into two 1-D DoG in x and y dimensions, and the level of scales in DoG pyramid is also reduced. The experiment shows that FG-SIFT reduces the computational complexity about 95% in GSS construction, also increases the accuracy of keypoint detection. Subsequently, the accuracy of generated features is increased 162%, and the accuracy of matched features is increased 8%. Apart from optimization in algorithm level, a hardware architecture of FG-SIFT's keypoint detection module is proposed. With a parallel architectural incorporating a five-stage pipeline, the execution time of keypoint detection is only 1.42ms@Xilinx Virtex5. Compared to conventional works, the speed is 21% faster than the fastest solution [9](ASIC), and hardware resources are 70% less than the most resources saved solutions [5] [6](Xilinx Virtex5).

In this paper, an affine invariance feature detection method based on Scale Invariant Feature Transform (SIFT) and Maximally Stable Extremal Regions (MSER) is proposed. Classical SIFT algorithm is not robust to affine deformations, because it is based on DOG detector which extracts circle regions for keypoint location. In order to overcome this disadvantage, DOG detector in conventional SIFT algorithm is replaced by MSER detector which is robust to affine deformation. Then these regions are normalized and extracted using SIFT. Simulation studies are carried out to show the effectiveness of the proposed method to affine transform in comparison to traditional SIFT algorithm.

The SIFT algorithm (Scale Invariant Feature Transform) proposed by Lowe [1] is an approach for extracting distinctive invariant features from images. It has been successfully applied to a variety of computer vision problems based on feature matching including object recognition, pose estimation, image retrieval and many others. However, in real-world applications there is still a need for improvement of the algorithm’s robustness with respect to the correct matching of SIFT features. In this paper, an improvement of the original SIFT algorithm providing more reliable feature matching for the purpose of object recognition is proposed. The main idea is to divide the features extracted from both the test and the model object image into several sub-collections before they are matched. The features are divided into several sub-collections considering the features arising from different octaves, that is from different frequency domains. The SIFT algorithm (Scale Invariant Feature Transform) proposed by Lowe [1] is an approach for extracting distinctive invariant features from images. It has been successfully applied to a variety of computer vision problems based on feature matching including object recognition, pose estimation, image retrieval and many others. However, in real-world applications there is still a need for improvement of the algorithm’s robustness with respect to the correct matching of SIFT features. In this paper, an improvement of the original SIFT algorithm providing more reliable feature matching for the purpose of object recognition is proposed. The main idea is to divide the features extracted from both the test and the model object image into several sub-collections before they are matched. The features are divided into several sub-collections considering the features arising from different octaves, that is from different frequency domains.

Road visual navigation relies on accurate road models. This study was aimed at proposing an improved scale-invariant feature transform (SIFT) algorithm for recovering depth information from farmland road images, which would provide a reliable path for visual navigation. The mean image of pixel value in five channels (R, G, B, S and V) were treated as the inspected image and the feature points of the inspected image were extracted by the Canny algorithm, for achieving precise location of the feature points and ensuring the uniformity and density of the feature points. The mean value of the pixels in 5×5 neighborhood around the feature point at an interval of 45o in eight directions was then treated as the feature vector, and the differences of the feature vectors were calculated for preliminary matching of the left and right image feature points. In order to achieve the depth information of farmland road images, the energy method of feature points was used for eliminating the mismatched points. Experiments with a binocular stereo vision system were conducted and the results showed that the matching accuracy and time consuming for depth recovery when using the improved SIFT algorithm were 96.48% and 5.6 s, respectively, with the accuracy for depth recovery of –7.17%-2.97% in a certain sight distance. The mean uniformity, time consuming and matching accuracy for all the 60 images under various climates and road conditions were 50%-70%, 5.0-6.5 s, and higher than 88%, respectively, indicating that performance for achieving the feature points (e.g., uniformity, matching accuracy, and algorithm real-time) of the improved SIFT algorithm were superior to that of conventional SIFT algorithm. This study provides an important reference for navigation technology of agricultural equipment based on machine vision. Keywords: scale-invariant feature transform (sift), feature matching, canny operator, energy method of feature point, farmland road, depth recovery, visual navigation DOI: 10.25165/j.ijabe.20191204.4821 Citation: Yao L J, Hu D, Yang Z D, Li H B, Qian M B. Depth recovery for unstructured farmland road image using an improved SIFT algorithm. Int J Agric & Biol Eng, 2019; 12(4): 141–147.

Image category recognition is important to access visual information on the level of objects and scene types. This paper presents an automatic recognition system of scene and object with PCA-SICEF feature for digital color images. SICEF (scale-invariant color and edge feature) is an extension of the conventional local SIFT (scale-invariant feature transform) feature, which only include edge invariance of local image region but not any color information. So the SIFT feature is not enough for distinguish image categorization especially for scene types, where the color information plays an important role for recognition. Therefore, we improve SIFT by including color feature for local image region, and name it as SICEF feature. However, the dimension of the extracted SICEF feature is so high that we use PCA (principle component analysis) to reduce the dimension, and then, use the PCA-domain SICEF (PCA-SICEF) for image classification. Experimental results show that it is much more efficient by our proposed PCA-SICEF feature than conventional SIFT feature.

Fully pipelined FPGA-based architecture for real-time SIFT extraction

A novel image registration method is proposed based on the scale-invariant feature transform (SIFT). Our approach combines the image frequency spectrum with a regular grid. The method exploits features of SIFT, the greater number of feature points in high-frequency areas of an image and regular grid traits with a fine spatial distribution to extract evenly distributed feature points. Global correspondence error checking is used to remove false matching pairs. The registration of eight groups of remote sensing images shows that our method has well-distributed feature points in the spatial and scale domains, obtains an average of 15.78% matching pairs more than uniform robust (UR)-SIFT, and provides better registration accuracy than SIFT and UR-SIFT.

The scale-invariant feature transform (SIFT) algorithm is still one of the most reliable image feature extraction methods. Despite its excellent robustness on various image transformations, SIFT's intensive computational burden has been severely preventing it from being used in real-time and energy-efficient embedded machine vision systems. To reduce processing time and energy cost while executing SIFT, an analog signal processing architecture, analog signal processing (ASP)SIFT, is proposed in this article. In ASP-SIFT, the Gaussian pyramid construction, difference-of-Gaussian (DoG) pyramid construction and keypoint locating, which are the primary steps of the keypoint detection part of the SIFT algorithm, are done directly with analog circuit networks. Thus, by completing keypoint detection in the analog domain, the total processing time is approximately equal to the settling time of the circuit network. Besides, by adopting a current-mode circuit network operating in the subthreshold region, the power dissipation would be very low. Simulation results show that the total processing speed for a typical video graphics array (VGA)-format (640 × 480) image is up to 2.3 kframes per second, which is at least 3.26× faster than the state-of-the-art digital hardware accelerators, while the system power is 94.5 mW and the energy consumption is only 40 μJ per frame.

A spatial-spectral SIFT for hyperspectral image matching and classification

The image data hiding technique can embed the secret message into the digital image. For military or medical applications the reversible data hiding technique is preferred because it offers the advantage to recover the original image after the message extraction, yet it still maintains the reversibility. In order to achieve reversibility, we propose a reversible data hiding algorithm that explores the spatial and frequency domains. Predictive coding is employed to embed the secret message in the spatial domain. The proposed algorithm applies an integer-to-integer transformation to convert the image originating in the spatial domain into the frequency domain. We then modify the high frequency coefficients only when embedding the secret message. Consequently, the low frequency coefficients are unchanged enabling the embedded image to preserve the image quality due to the hidden message. In addition, the algorithm further increases the embedding capacity because it takes advantage of both the spatial and frequency domains. Keywords-Data hiding; reversible data embedding; predictive coding; wavelet transform

Computerized human face recognition is a complex task of deformable pattern recognition. The principal source of complexities lies in the significant inter-class overlapping of faces due to the variations caused by different poses, illuminations, and expressions (PIE). The popularly used computerized face recognition algorithms like PCA, EBGM etc. are fairly reliable to determine facial attributes from an image. But, in most of the cases the features are extracted in terms of gray textures. When the database size is tuned to millions, then huge processing time is required, as each of the pixel must be represented using at least eight bits. In the present paper, our objective is to minimize the processing time by reducing the number of bits to represent each pixel. This we have done by combining two methods. The first one is a neuro-visually inspired method of figure-ground segregation (NFGS) which can convert the entire face image into a binary 2D array, efficiently. The second one is the scale invariant feature transform (SIFT) which extracts the scale invariant and rotation invariant features from the binarized face image and thereafter matches the features. The proposed algorithm is found successful in actually enhancing the performance of face matching. Psycho-visual experiments also corroborate the fact.

The SIFT (scale invariant feature transform) has demonstrated its superior performance in identifying transformed images over many other approaches. However, both of its detection and matching stages are expensive, because a large number of keypoints are detected in the scale-space and each keypoint is described using a 128-dimensional vector. We present two possible solutions for feature-point reduction. First is to down scale the image before the SIFT keypoint detection and second is to use corners (instead of SIFT keypoints) which are visually significant, more robust, and much smaller in number than the SIFT keypoints. Either the curvature descriptor or the highly distinctive SIFT descriptors at corner locations can be used to represent corners.We then describe a new feature-point matching technique, which can be used for matching both the down-scaled SIFT keypoints and corners. Experimental results show that two feature-point reduction solutions combined with the SIFT descriptors and the proposed feature-point matching technique not only improve the computational efficiency and decrease the storage requirement, but also improve the transformed image identification accuracy (robustness).

Synthetic aperture radar (SAR) image target recognition has important application values in security reconnaissance and disaster monitoring. However, due to speckle noise and target orientation sensitivity in SAR images, traditional spatial domain recognition methods face challenges in accuracy and robustness. To effectively address these challenges, we propose a dual-branch spatial-frequency domain fusion recognition method with cross-attention, achieving deep fusion of spatial and frequency domain features. In the spatial domain, we propose an enhanced multi-scale feature extraction module (EMFE), which adopts a multi-branch parallel structure to effectively enhance the network’s multi-scale feature representation capability. Combining frequency domain guided attention, the model focuses on key regional features in the spatial domain. In the frequency domain, we design a hybrid frequency domain transformation module (HFDT) that extracts real and imaginary features through Fourier transform to capture the global structure of the image. Meanwhile, we introduce a spatially guided frequency domain attention to enhance the discriminative capability of frequency domain features. Finally, we propose a cross-domain feature fusion (CDFF) module, which achieves bidirectional interaction and optimal fusion of spatial-frequency domain features through cross attention and adaptive feature fusion. Experimental results demonstrate that our method achieves significantly superior recognition accuracy compared to existing methods on the MSTAR dataset.