Analysis of accuracy factor and pre-processing methodology of image compensation for 3D reconstruction using 2D image obtained from unmanned aerial vehicle (UAV)

Figures & data

Figure 1. Input 2D image, calculation of camera pose, generation of 3D point cloud.

Figure 2. Image histogram process.

Figure 3. Image compensation methodologies.

Figure 4. Specification of UAV and camera.

Figure 5. Comparison of photogrammetry software.

Figure 6. Pre-processing software (Matlab).

Figure 7. Test condition(target1(left), target2(right)).

Figure 8. Compensation of 2D images.

Figure 9. The results of sparse point cloud.

Figure 10. The results of dense point cloud.

Table 1. Application possibilities for digital twin.

Shutter speed (sec)	1/2000	1/6000	1/500	1/200	1/2000	1/6000	1/500	1/200
Aperture values	F13	F8	F22	F22	F13	F8	F22	F22
Average brightness (lux)	100	120	150	200	100	120	150	200
Pixel	157464	157464	157464	157464
Test Target and acquired images
Number of point cloud	1,269	1,059	1,180	1,349	1,269	1,059	1,180	1,349

Table 2. Comparison of sparse point cloud number according to pre-processing variables.

	Variable	Target 1	Target 2
AHE	celv = 0.005	58,139	68,213
	celv = 0.01	60,614	69,935
	celv = 0.02	64,184	70,993
IS	a = 0.5, r = 1	49,642	60,348
	a = 1, r = 1	44,413	55,815
	a = 1.5, r = 1	40,578	51,598
	a = 0.5, r = 0.5	52,875	63,693
	a = 0.5, r = 1	49,642	60,348
	a = 0.5, r = 1.5	47,169	57,743
LCE	a = 0, e = 0.3	54,536	65,166
	a = 0.5, e = 0.3	58,326	69,960
	a = 1, e = 0.3	62,271	72,852
	a = 0.5, e = 0.3	58,326	69,960
	a = 0.5, e = 0.6	56,924	68,582
	a = 0.5, e = 0.9	55,630	66,909

celv: contrast enhancement limit value, a = amount, r = radius, e = edgeThreshold.

Table 3. Paired sample T-test between original 2D images and compensated 2D images.

	Paired Differences					t	df	Sig.(2-tailed)
	Mean	Std. Deviation	Std. Error Mean	95% Confidence Interval of the Difference
				Lower	Upper
Original -AHE (Target1)	−5608. 00000	2718. 15011	1109. 68013	−8460. 52360	−2755. 47640	−5.054	5	.004
Original -IS (Target1)	7984. 50000	4371. 33557	1784. 59028	3397. 06465	12571. 93535	4.474	5	.007
Original -LCE (Target1)	−3404. 66667	3041. 13641	1241. 53874	−6596. 14360	−213.18973	−2.742	5	.041
Original -AHE (Target2)	−3704. 66666	1255.01914	512. 35942	−5021. 72849	−2387. 60484	−7.231	5	.001
Original -IS (Target2)	18622. 50000	4371. 33557	1784.590275	14035.06465	23209.93534	10.435	5	.000
Original -LCE (Target2)	−2895. 83333	2678.55650	1093. 51611	−5706. 80599	−84. 86067	−2.648	5	.046

Mean: The average difference between the two variables.

Standard deviation: The standard deviation of the difference scores.

Standard error mean: The standard error.

t: The paired T test statistic.

df: The degrees of freedom for this test.

Sig. (2-tailed): The p-value corresponding to the given test statistic t.