Color Speckle Research Articles

Multi-channel computational ghost imaging based on multi-scale speckle optimization

A multi-channel computational ghost imaging (GI) method based on multi-scale speckle optimization is proposed. We not only reduce imaging time and enhance imaging quality but also reduce interference among different channels. Using one bucket detector to receive total light intensity, the color speckle is formed by combining components obtained through the singular value decomposition of three self-designed multi-scale measurement matrices. Simulation and experimental results demonstrate that our designed method contributes to reducing imaging time and enhancing imaging quality, achieving improved visual quality even at low sampling rates. This approach enhances GI flexibility and holds potential for diverse applications, including target recognition and biomedical imaging.

A 3D Reconstruction Method Based on Homogeneous De Bruijn-Encoded Structured Light

Structured light three-dimensional reconstruction is one of the important methods for non-contact acquisition of sparse texture object surfaces. Variations in ambient illumination and disparities in object surface reflectance can significantly impact the fidelity of three-dimensional reconstruction, introducing considerable inaccuracies. We introduce a robust method for color speckle structured light encoding, which is based on a variant of the De Bruijn sequence, termed the Homogeneous De Bruijn Sequence. This innovative approach enhances the reliability and accuracy of structured light techniques for three-dimensional reconstruction by utilizing the distinctive characteristics of Homogeneous De Bruijn Sequences. Through a pruning process applied to the De Bruijn sequence, a structured light pattern with seven distinct color patches is generated. This approach ensures a more equitable distribution of speckle information.

Statistical Analysis of RGB Speckle Grains for Simulating Color Speckle Distributions

Statistical Analysis of RGB Speckle Grains for Simulating Color Speckle Distributions

Digital Image Correlation with a Prism Camera and Its Application in Complex Deformation Measurement.

Given the low accuracy of the traditional digital image correlation (DIC) method in complex deformation measurement, a color DIC method is proposed using a prism camera. Compared to the Bayer camera, the Prism camera can capture color images with three channels of real information. In this paper, a prism camera is used to collect color images. Relying on the rich information of three channels, the classic gray image matching algorithm is improved based on the color speckle image. Considering the change of light intensity of three channels before and after deformation, the matching algorithm merging subsets on three channels of a color image is deduced, including integer-pixel matching, sub-pixel matching, and initial value estimation of light intensity. The advantage of this method in measuring nonlinear deformation is verified by numerical simulation. Finally, it is applied to the cylinder compression experiment. This method can also be combined with stereo vision to measure complex shapes by projecting color speckle patterns.

P‐15.3: Color Speckle Evaluation Using Eigenvalues Method

In the current international standard (IEC 62906‐5‐4), the variance and covariance of color coordinates u’ and v’, as well as photometric speckle contrast are used to evaluate color speckle. There are some shortcomings in the covariance method that it is difficult for users to match the speckle distribution with covariance intuitively. In this paper, the eigenvalues of the sample covariance matrix generated by u’ and v’ are proposed to evaluate color speckle, which can be more intuitive and more suitable as an evaluation metric in measurement.

Comparison Reproducibility of Measured and Calculated Color Speckle Distributions in CIE xyY Color Space

Comparison Reproducibility of Measured and Calculated Color Speckle Distributions in CIE xyY Color Space

Real single-channel color image encryption method based on computational ghost imaging

A real single-channel color image encryption method based on computational ghost imaging is proposed. Compared with the currently proposed color single-channel encryption scheme, the method does not decompose the color image into three gray-scale images or encode it into a grayscale image for encryption. Instead, the color speckle patterns are used as the key to directly encrypt. The ciphertext is a grayscale image and thus has camouflage properties to a certain extent. Furthermore, the optical encryption setup is easy to be implemented and the key is generated by a chaotic system, which not only guarantees security but also reduces the volume of key transmission. The feasibility and high security of this method are supported by both computer simulations and optical experiments.

A bilayer color digital image correlation method for the measurement of the topography of a liquid interface

One of the most essential characteristics of the liquid interface is the topography dominated by hydrodynamics or capillary effects. Although there have developed 3D imaging techniques for the measurement of such topography, their setups, operations and reconstructions are relatively complex and suffer from low efficiency. Here we report a bilayer color digital image correlation (BC-DIC) method for the measurement of the topography of a liquid interface. The basic principle of the new method is the refraction of beneath bilayer color speckle patterns at the liquid interface, which makes it possible to perform 3D reconstruction through 2D measurement of the virtual displacement field of the speckle patterns. The equations for BC-DIC in different situations are deduced and discussed in detailed. Validation experiments are carried out to reconstruct the topography of triangular prism, planoconvex, complex transparent surface and sloshing water surface. The results show that BC-DIC is feasible and accurate for measuring the topography of transparent objects, including liquid interface. This new method paves the way for investigating surface and interface phenomena, such as capillarity and wetting issues, hydrodynamics on liquid interface, etc.

Deformation Measurement of Scaling and Rotation Objects Based on Digital Image Correlation Method with Color Information

The digital image correlation (DIC) method is widely used in deformation measurement due to the advantages of being non-contact, high precision, full field measurement, and requiring simple experimental equipment. Traditionally, the grayscale speckle patterns captured by a monochromatic camera are used in the DIC method. With the growing development of consumer color cameras, there is a great potential for developing color information in the DIC method. This paper proposes a scaling- and rotation-invariant DIC (SRI-DIC) method based on the color speckle patterns. For the integer-pixel matching stage, the scaling- and rotation-invariant color histogram feature is used to estimate the initial value of the deformation parameters. For the sub-pixel matching stage, a new error function using the three-channel information of color camera is proposed to avoid the influence of illumination changes. In addition, this paper proposes a reverse retrieve strategy instead of the forward search to reduce the search time. Experiments show that the proposed SRI-DIC algorithm not only has scaling and rotation invariance, robustness, and high efficiency, but also that the average accuracy of the strain result can reach 0.1%.

Nonuniformity Measurement of Image Resolution under Effect of Color Speckle for Raster-Scan RGB Laser Mobile Projector

Nonuniformity Measurement of Image Resolution under Effect of Color Speckle for Raster-Scan RGB Laser Mobile Projector

Temperature Dependence Measurement of Color Speckle for Projected Fiber-out White Laser Beam from RGB Laser Module

Temperature Dependence Measurement of Color Speckle for Projected Fiber-out White Laser Beam from RGB Laser Module

Temperature Dependence Measurement of Color Speckle for Projected Fiber-out White Laser Beam from RGB Laser Module

Temperature Dependence Measurement of Color Speckle for Projected Fiber-out White Laser Beam from RGB Laser Module

An error elimination method for high-temperature digital image correlation using color speckle and camera

Digital image correlation method is a kind of displacement and strain measurement technique based on visible light illumination. It can realize non-contact and full-field measurement with lower requirements on the measurement environment, thus it's widely used in testing and research for mechanical properties of materials at high temperature. But there are many factors affecting the measurement accuracy due to the complexity of the high temperature environment, of which the influence of the thermal disturbance on digital image correlation method is the most obvious. In order to reduce the influence of it and improve the measurement accuracy, this paper proposes a measurement method for eliminating thermal disturbance error in high temperature deformation measurement based on color speckle and camera. Two kinds of grayscale field information of different colors were endued to the surface of specimen, and we collected images by color camera with channel separation for each frame of them. Then we processed the grayscale field of two channels separately combined with the digital image correlation method, analyzed the information carried by two different grayscale fields, and a simple mathematical model was performed to separate the thermal disturbance error from the measurement results. Finally, we set up the experimental system, built the mathematical model between the two channels through static measurement experiment, which was used to extract and correct the thermal disturbance error of measurement results of the rigid body motion experiment. The high consistency between corrected result and true displacement value proved the feasibility and accuracy of the proposed method.

Visual resolution of raster-scan laser mobile projectors under effects of color speckle

Visual resolution of raster-scan, laser mobile projectors using red, green, blue (RGB) laser diodes was measured using a high-speed 2D speckle measurement equipment, considering the effects of color speckle. Blind evaluation of three laser mobile projectors was carried out. Photometric visual resolution of white point was obtained by calculating contrast modulation CM using a grille pattern of narrowing line-pairs. The color speckle distribution was plotted in CIE 1931 chromaticity diagram and in CIELab color space. The color speckle was found to degrade photometric visual resolution, as well as the color speckle distribution spreading in the color spaces. Color shifts at the edge of the line image were obviously observed by the color speckle plots in the color spaces. The color shifts are found to be generated due to RGB LD switch timing mismatches. As a result, one of them achieved better performance than the others. This 2D color speckle measurement method is indispensable for measuring visual resolution of laser displays, reproducing speckle grain sizes on human retina.

Color speckle measurement errors using system with XYZ filters

Measurement errors of color speckle are analyzed for a measurement system equipped with revolving XYZ filters and a 2D sensor. One of the errors is caused by the filter characteristics unfitted to the ideal color matching functions. The other is caused by uncorrelations among the optical paths via the XYZ filters. The unfitted color speckle errors of all the pixel data can be easily calibrated by conversion between the measured BGR chromaticity triangle and the true triangle obtained by the BGR wavelength measurements. For the uncorrelated errors, the measured BGR chromaticity values spread over around the true values. As a result, it would be more complicated to calibrate the uncorrelated errors, repeating the triangular conversion pixel by pixel. Color speckle and its errors greatly affect also chromaticity measurements and image quality of displays using coherent light sources.

10-2: Direct Measurement of Color Speckle Applying XYZ Filters

10-2: Direct Measurement of Color Speckle Applying XYZ Filters

Polychromatic speckle reduction in laser pico-projectors using stationary dual Hadamard diffusers

Speckle from coherent light sources continues to be a limiting factor in the design and manufacturing of laser projectors. Utilizing diffractive diffusers has been an effective method for reducing monochromatic speckle contrast. Color laser projection devices require the use of red, green, and blue laser sources therefore; using a monochromatic diffractive diffuser may not be optimal for color speckle contrast reduction. A new static dual-diffuser system utilizing Hadamard matrices has been designed to reduce full color speckle. This paper analyzes the effectiveness of the new Hadamard diffusers in reducing speckle using three separate RGB laser diodes. A simulation of the Hadamard diffusers is conducted to determine the optimum spacing between the two diffusers for polychromatic speckle reduction. Experimental measured results are presented using the optimal spacing of Hadamard diffusers for RGB color speckle reduction showing 60% reduction in contrast.

Color Speckle

Color Speckle

Color speckle

Color speckle