Digital Fringe Projection Method Research Articles

Warpage characterization of a large size fan-out panel subjected to inhomogeneous heating by a digital fringe projection system

Warpage is an essential issue of fan-out wafer/panel level packaging. Increasing size of wafers/panels poses new challenges to the warpage characterization system. In this work, a warpage measurement system based on digital fringe projection method is reported. It can cover 600 mm × 600 mm area with 4 × 4 camera array. Benchmark tests were carried out to evaluate the measurement error, which was found to be 0.053 %. The warpage evolution of a 515 mm × 510 mm panel with inhomogeneous heating was then studied by heating from room temperature to 90 °C. It was found that the warpage evolution of a large size panel can be very complex. Based on finite element modeling results, this can be attributed to temperature gradient, and several other factors, including mismatch of coefficient of thermal expansion, gravity, initial stress state and original layout design of the panel (such as size and count of chips, RDL design and chip position).

Adaptive Fringe Projection for 3D Shape Measurement with Large Reflectivity Variations by Using Image Fusion and Predicted Search

There is always a great challenge for the structured light technique that it is difficult to deal with the surface with large reflectivity variations or specular reflection. This paper proposes a flexible and adaptive digital fringe projection method based on image fusion and interpolated prediction search algorithm. The multiple mask images are fused to obtain the required saturation threshold, and the interpolated prediction search algorithm is used to calculate the optimal projection gray-level intensity. Then, the projection intensity is reduced to achieve coordinate matching in the unsaturated condition, and the adaptive digital fringes with the optimal projection intensity are subsequently projected for phase calculation by using the heterodyne multifrequency phase-shifted method. The experiments demonstrate that the proposed method is effective for measuring the high-reflective surface and unwrapping the phase in the local overexposure region completely. Compared with the traditional structured light measurement methods, our method can decrease the number of projected and captured images with higher modulation and better contrast. In addition, the measurement process only needs two prior steps and avoids hardware complexity, which is more convenient to apply to the industry.

Real-time subtraction-based calibration methods for deformation measurement using structured light techniques.

Calibration of the optical trigonometric relationships in structured light is essential for the accuracy of out-of-plane displacement measurement. A simple calibration mechanism based on real-time image subtraction is proposed. Details of calibrating the height-to-phase ratio of the digital fringe projection method, the relationship between out-of-plane and in-plane displacements of the digital projection-speckle correlation method, and the scale factor of the optical system are described. The calibration methods are applied to the deformation measurement of a clamped Plexiglas plate, which demonstrates the effectiveness of the calibration methods. The real-time subtraction-based calibration methods provide alternatives for calibrating structured light techniques used for out-of-plane displacement measurement.

EFFECT OF DIGITAL FRINGE PROJECTION PARAMETERS ON 3D RECONSTRUCTION ACCURACY

Abstract. 3D reconstruction has been already one of the most interesting research areas among photogrammetry and computer vision researchers. This thesis aims to evaluate digital fringe projection method in reconstruction of small objects with complicated shape. Digital fringe projection method is a novel method in structured light technique which integrates interferometric and triangulation methods. In this method, a digital projector projects a series of sinusoidal fringe patterns onto the object surface. Then, a camera from a different point of view captures images of patterns that are deformed due to object's surface topography. Afterward, the captured images will be processed and the depth related phase would be calculated. Due to using arctangent function in the process of phase extraction, the computed phase ranges from –pi to +pi, so a phase unwrapping step is necessary. Finally, the unwrapped phase map would be converted to depth map with some mathematical models. This method has many advantages like high speed, high accuracy, low cost hardware, high resolution (each pixel will have a depth at end), and simple computations. This paper aims to evaluate different parameters which affect the accuracy of the final results. For this purpose, some test were designed and implemented. These tests assess the number of phase shifts, spatial frequency of the fringe pattern, light condition, noise level of images, and the color and material of target objects on the quality of resulted phase map. The evaluation results demonstrate that digital fringe projection method is capable of obtaining depth map of complicated object with high accuracy. The contrast test results showed that this method is able to work under different ambient light condition; although at places with high light condition will not work properly. The results of implementation on different objects with various materials, color and shapes demonstrate the high capability of this method of 3D reconstruction.

Comparison of Validated Assessment Scales and 3D digital fringe projection method to assess lifetime development of wrinkles in men

The assessment of wrinkle severity is an important evaluation criterion to determine the efficacy of aesthetic treatments. Aim of the present study was to compare Validated Assessment Scales (VAS) and 3D fringe projection (PRIMOS(®) ) for the evaluation of facial wrinkles in men and to determine standard values for each level of the VAS. 150 male subjects (20 to 70 years) were selected following strict criteria. Wrinkle severity at periorbital, glabella and forehead lines was evaluated using the 3D fringe projection and 5-point photonumeric VAS. The results of both methods were matched by determining quantitative values for each level of the clinical rating scale. High average correlation with age was found for VAS, Wd, maxWd, lWd, Wv, aWa and pWa. With a Wd of 60 to 70μm crow's feet and forehead lines are pronounced first, whereas glabella lines develop in subject's mid-forties, by an Wd of 180μm. Wrinkle severity increases at all locations every 10 years of age by one level of the VAS. This increase corresponds to an increase of Wd about 100 μm at glabella and forehead lines, and about 50 μm at crow's feet. The presented reference values for the Validated Assessment Scale are an important step towards an optimized assessment of skin aging and aesthetic dermatological treatments. The data helps to combine the precession of a biophysical measurement with the practical relevance of a clinical rating.