Noise Filter Reducing Deformation in Digital Holography

Advanced Engineering Forum ◽

10.4028/www.scientific.net/aef.38.71 ◽

2020 ◽

Vol 38 ◽

pp. 71-75

Author(s):

Yoshitaka Takahashi ◽

Takaya Okada ◽

Ryutaro Sekiguchi ◽

Madoka Fukushima

Keyword(s):

Phase Difference ◽

Digital Holography ◽

Phase Shifting ◽

Shape Measurement ◽

Difference Image ◽

Noise Filter ◽

Contact Shape

A phase difference image using phase-shifting digital holography, which is applied for non-contact shape measurement, contains speckle noises and filtering to reduce them is inevitable for its application. We have developed a new filter which causes less deformation than commonly used filters.

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Noise Filter for Surface Shape Measurement in Digital Holography

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.888.47 ◽

2019 ◽

Vol 888 ◽

pp. 47-51 ◽

Cited By ~ 1

Author(s):

Yoshitaka Takahashi ◽

Masakazu Shingu ◽

Masatoshi Saito ◽

Toru Nakajima ◽

Ryutaro Sekiguchi ◽

...

Keyword(s):

Digital Holography ◽

Moving Average ◽

Speckle Noise ◽

Surface Shape ◽

Shape Measurement ◽

Shape Information ◽

Difference Image ◽

Noise Filter ◽

Contact Shape ◽

Average Filter

Phase difference image using phase-shifting digital holography is one of the prospective methods for non-contact shape measurement. For the application, filtering of the obtained image is needed to reduce the speckle noise. Conventional filter, e.g. moving average filter, causes loss of the shape information especially around the region with high steepness. To solve this problem novel filter has been developed that kept steepness of the shape in noise reduction. The filtered data were compared with conventionally filtering ones and the former was closer to the data observed by a laser measuring microscope.

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Combined Reduced Phase Dual-Directional Illumination Digital Holography and Speckle Displacements for Shape Measurement

International Journal of Optics ◽

10.1155/2019/4906109 ◽

2019 ◽

Vol 2019 ◽

pp. 1-6

Author(s):

Davood Khodadad

Keyword(s):

Phase Difference ◽

Digital Holography ◽

Relative Phase ◽

Groove Depth ◽

Phase Unwrapping ◽

Shape Measurement ◽

Phase Ambiguity ◽

Holographic Method ◽

Height Range ◽

Phase Differences

We present a digital holographic method to increase height range measurement with a reduced phase ambiguity using a dual-directional illumination. Small changes in the angle of incident illumination introduce phase differences between the recorded complex fields. We decrease relative phase difference between the recorded complex fields 279 and 139 times by changing the angle of incident 0.5° and 1°, respectively. A two cent Euro coin edge groove is used to measure the shape. The groove depth is measured as ≈300 μm. Further, numerical refocusing and analysis of speckle displacements in two different planes are used to measure the depth without a use of phase unwrapping process.

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Determination of Phase Shift by Digital Holography

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.888.43 ◽

2019 ◽

Vol 888 ◽

pp. 43-46

Author(s):

Yoshitaka Takahashi ◽

Masatoshi Saito ◽

Toru Nakajima ◽

Masakazu Shingu

Keyword(s):

Phase Shift ◽

Noise Reduction ◽

Digital Holography ◽

High Accuracy ◽

Measured Data ◽

Phase Shifting ◽

Surface Shape ◽

Shape Measurement ◽

Phase Shifting Interferometry

In phase shifting interferometry phase shift is applied by various ways, but applying it with high accuracy, especially by LD current modulation, is not easy. In order to determine the accurate phase shift a new method has been proposed that the value of LD current corresponding to π/2 phase shift can be determined by phase shifting digital holography. The measured data of standard in surface shape measurement were used for calibration, and the obtained value was confirmed to cause noise reduction and improvement of holographic reconstructed images in digital holography.

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