Focus Measure Operator Combining Cosine Transform and Laplacian Operator

Fig. 7. Figures of experimental device. (a) Target scanning experiment device figure with lens of f=8 mm; (b) sensor scanning experiment device figure with lens of f=8 mm; (c) sensor scanning experiment device figure with microscope lens of NA=0.65

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Fig. 8. Partial defocused images. (a) Defocused image obtained by moving the target under the imaging lens; (b) defocused image obtained by moving the sensor under the imaging lens; (c) defocus image obtained by moving the sensor under the microscope lens; (d) defocused images obtained through lens zoom

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Fig. 9. Focus evaluation curves of experimental defocused image. (a) A(222,333); (b) B(380,310); (c) C(290,240); (d) D (180,90)

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Table 1. Parameter definitions and description

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Table 1. Parameter definitions and description

Symbol	Description	Formula
λ	Wavelength
NA	Numerical aperture
k	Wave number	k=2π/λ
f_c	System cut-off frequency	f_c=2NA/λ
q	Radial spatial frequency	q= $\sqrt[]{u^{2} + v^{2}}$ ,u,v∈[-f_c,f_c]
jinc(x)		jinc(x)=2J₁(x)/x
β		β=arccos(q/f_c)
z	Defocus distance of the object plane

Table 2. Calculation results of simulated defocus image

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Table 2. Calculation results of simulated defocus image

Method	S_e				S_p
Method	A	B	C	Mean value	A	B	C	Mean value
GEN	0.005	0.061	0.038	0.035	1.51	1.86	1.90	1.76
GLV	0.047	0.055	0.032	0.044	0.66	1.85	1.78	1.43
SWAV	0.004	0.032	0.025	0.020	1.42	1.66	1.67	1.58
SML	0.003	0.017	0.061	0.027	1.51	1.68	1.54	1.57
DCT	0.009	0.031	0.119	0.053	1.90	1.80	1.84	1.85
Proposed method	0.086	0.148	0.245	0.159	2.63	2.27	3.11	2.67

Table 3. Device parameters used in the experiment

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Table 3. Device parameters used in the experiment

Device	Parameter
Sensor	Company / Name	Vieworks / VH-310C
	Pixel size	7.4 μm×7.4 μm
	Active image size	640×480
	Bit	12 bit, (0--4096)
Lens	Company	Computar
	Focal length	2.4--16 mm
	F-number	2.4
Microscope	Numerical aperture	0.65
Microscope	Magnification	40
Linear stage	Company / Name	PI / M-403.8DG
	Resolution	0.5 μm
	Travel range	200 mm

Table 4. Calculation results of experimental defocus image

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Table 4. Calculation results of experimental defocus image

Method	S_e				S_p
Method	A	B	C	Mean value	A	B	C	Mean value
GEN	0.190	0.052	0.118	0.703	1.349	0.165	0.185	1.180
GLV	0.076	0.015		0.655	1.194	0.073		0.746
SWAV	0.106	0.209	0.091	0.557	1.228	0.122	0.161	0.355
SML	0.096	0.116	0.250	0.375	1.181	0.156	0.145	0.317
DCT	0.208	0.012	0.400	0.756	1.392	0.287	0.275	1.223
Proposed method	0.303	0.734	0.839	0.973	1.816	1.313	1.965	1.993

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Xiufeng Wang, Xiaowei Sun, Jiake Wang, Xu Gao, Hang Yang. Focus Measure Operator Combining Cosine Transform and Laplacian Operator[J]. Laser & Optoelectronics Progress, 2021, 58(24): 2410005

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Paper Information

Category: Image Processing

Received: Dec. 28, 2020

Accepted: Mar. 8, 2021

Published Online: Nov. 24, 2021

The Author Email: Sun Xiaowei (sxwlux@163.com)

DOI:10.3788/LOP202158.2410005

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology