Vibration frequency measurement using a local multithreshold technique

Espinosa, Julián; Roig, Ana B.; Pérez, Jorge; Mas, David

doi:10.1364/oe.21.026198

Cited by 33 publications

(39 citation statements)

References 12 publications

(11 reference statements)

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“…As we stated above, according to what is established in [4], special objects can be tracked with accuracy of the order of 1/N. This affirmation was proved through numerical simulations and with different error criteria.…”

Section: Proposalsupporting

confidence: 66%

“…In [3], the authors revisited the idea and show that, by using convenient targets, the theoretical maximum accuracy is of the order of 1/N px, being N the total number of pixels in the scene. Although these targets are of difficult implementation, they may be useful to analyze the efficiency of different implementations and even to design new methods [4].…”

Section: Introductionmentioning

confidence: 99%

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Realistic limits for subpixel movement detection

2016

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Object tracking with subpixel accuracy is of fundamental importance in many fields since it provides optimal performance at relatively low-cost. Although there are many theoretical proposals that lead to resolution increments of several orders of magnitude, in practice, this resolution is limited by the imaging systems. In this paper we propose and demonstrate through simple numerical models a realistic limit for subpixel accuracy. The final result is that maximum achievable resolution enhancement is connected with the dynamic range of the image, i.e. the detection limit is 1/2^(nr.bits). The results here presented may help to proper design of superresolution experiments in microscopy, surveillance, defense and other fields.

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Section: Proposalsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Realistic limits for subpixel movement detection

2016

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“…The use of accelerometers is sometimes dismissed because of the complexity or accessibility of the specimen to be measured, whereas a laser vibrometer's high cost is still a major drawback in most cases. Thus, computer vision systems [2][3][4][5][6][7][8] have been demonstrated to be a reliable alternative to traditional methods in the last few years. Independently, whether or not they use object recognition, vision-based methods assume that object movement or vibration can be perceived through changes in the light reflected or diffused by a moving target.…”

Section: Introductionmentioning

confidence: 99%

“…After presenting the mathematical basis of the technique [12] and discussing the maximum theoretical subpixel resolution achievable, in [5], the authors demonstrated the possibility of measuring the vibration frequency of objects in a high-speed video sequence simply by counting luminance changes in local regions. The proposal consisted of selecting a local neighborhood or region of interest and applying a multilevel binary threshold to the image within this region.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we go beyond [5] and propose a technique to track the subpixel movement of an object besides using its frequency of vibration and without using target or template matching, but with the specific need of the object image to have two nonparallel straight segments and limited to in-plane translation. The manuscript is structured as follows.…”

Section: Introductionmentioning

confidence: 99%

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Method for targetless tracking subpixel in-plane movements

2015

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We present a targetless motion tracking method for detecting planar movements with subpixel accuracy. This method is based on the computation and tracking of the intersection of two nonparallel straight-line segments in the image of a moving object in a scene. The method is simple and easy to implement because no complex structures have to be detected. It has been tested and validated using a lab experiment consisting of a vibrating object that was recorded with a high-speed camera working at 1000 fps. We managed to track displacements with an accuracy of hundredths of pixel or even of thousandths of pixel in the case of tracking harmonic vibrations. The method is widely applicable because it can be used for distance measuring amplitude and frequency of vibrations with a vision system.

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Developments with Motion Magnification for Structural Modal Identification Through Camera Video

Chen

Wadhwa

Durand

et al. 2015

Conference Proceedings of the Society for Experimental Mechanics Series

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Non-contact measurement of the response of vibrating structures may be achieved using several different methods including the use of video cameras that offer flexibility in use and advantage in terms of cost. Videos can provide valuable qualitative information to an informed person, but quantitative measurements obtained using computer vision techniques are essential for structural assessment. Motion Magnification in videos refers to a collection of techniques that amplify small motions in videos in specified bands of frequencies for visualization, which can also be used to determine displacements of distinct edges of structures being measured. We will present recent developments in motion magnification for the modal identification of structures. A new algorithm based on the Riesz transform has been developed allowing for real-time application of motion magnification to normal-speed videos with similar quality to the previous computationally intensive phase-based algorithm. Displacement signals are extracted from strong edges in the video as a basis for the data necessary for modal identification. Methodologies for output-only modal analysis applicable to the large number of signals and short length signals are demonstrated on example videos of vibrating structures. Keywords Computer vision • Non-contact • Modal identification • Mode shape • Motion magnification IntroductionNon-contact techniques for measuring structures have only recently been available as a serious option. Laser vibrometers provide an accurate way of measuring the surface velocity of an object and are now widely used as the gold standard for non-contact vibration measurement [1]. For large structures, scanning laser vibrometers have the capability of measuring a large number of points in succession, however for phased measurements they require another stationary laser vibrometer to serve as a reference, or they must be continuously scanning systems [2]. Laser vibrometer arrays consisting of multiple laser vibrometers measuring simultaneously are also an option [3]. However in general, laser vibrometers may be prohibitively expensive for many applications.Video cameras collect light from a scene of interest onto a sensor consisting of an array of pixels and can obtain data with high spatial density. Interpretation of this data can be complex, especially to translate a video into quantitative measurement of the vibration and displacements of a structure. Computer vision techniques and digital image correlation have been successfully used to measure displacements of structures and quantify vibrations in structures [4][5][6][7][8].This paper presents developments in structural modal identification in videos using the family of algorithms called motion magnification [9][10][11]. These algorithms can visualize operational deflections shapes (ODS) in a vibrating structure by magnifying motions in a video in a particular frequency band [12]. The most recent development of interest is the development of a Riesz transform based method that allow...

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Vibration frequency measurement using a local multithreshold technique

Cited by 33 publications

References 12 publications

Realistic limits for subpixel movement detection

Realistic limits for subpixel movement detection

Method for targetless tracking subpixel in-plane movements

Developments with Motion Magnification for Structural Modal Identification Through Camera Video

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