Laser & Optoelectronics Progress, Volume. 62, Issue 16, 1630001(2025)
Herbicide Stain Detection with Terahertz Imaging Combined with Image Enhancement
Figures & Tables(24)
Fig. 1. System diagram (upper: reflection mode; lower: through-transmission mode)
Fig. 3. Photos of samples of group 1 (volume fractions of lower row from left to right are 10%, 20%, 30%, 40%, 50%; volume fractions of upper row from left to right are 60%, 70%, 80%, 90%, 100%)
Fig. 4. Terahertz images of samples of group 1 (volume fraction order is as shown in Fig. 3). (a) Time-domain spectral images; (b) spectral images in 0‒0.5 THz frequency band; (c) spectral images in 0.5‒1.7 THz frequency band; (d) spectral images in 1.0‒2.7 THz frequency band
Fig. 5. Terahertz images of samples of group 2. (a1)‒(a25) are photos of samples; (b1)‒(b25) are time-domain spectral images; (c1)‒(c25) are spectral images in 0‒0.5 THz frequency band; (d1)‒(d25) are spectral images in 0.5‒1.5 THz frequency band
Fig. 7. Terahertz images of sample freshd31. (a) Photo of sample; (b) time-domain spectral image; (c) spectral image in 0‒0.5 THz frequency band; (d) spectral image in 0.5‒1.0 THz frequency band
Fig. 8. Terahertz images of samples of group 4. (a1)‒(a5) are photos of samples; (b1)‒(b5) are time-domain spectral images; (c1)‒(c5) are spectral images in 0‒0.5 THz frequency band; (d1)‒(d5) are spectral images in 0.5‒1.7 THz frequency band; (e1)‒(e5) are spectral images in 1.0‒2.7 THz frequency band
Fig. 9. Terahertz images and their pseudo color images. (a1)‒(a12) are terahertz images; (b1)‒(b12) are their pseudo color images
Fig. 10. Terahertz images and their contrast adjustment images. (a1)‒(a12) are terahertz images; (b1)‒(b12) are their contrast adjustment images
Fig. 11. Enhancement results of terahertz images with the highest contrast for pants samples. (a) Terahertz images; (b) images after median filtering; (c) images after histogram equalization; (d) images after sharpening
Fig. 12. Otsu image segmentation results of terahertz images with the highest contrast for each sample. (a1)‒(a5) are terahertz images; (b1)‒(b5) are images after Otsu
Table 1. Statistical table of herbicides
View tableTable 1. Statistical table of herbicides
No. Name of herbicide Form Manufacturer 1 Glyphosate Water-based solution Tianjin Huayu Pesticide Co.， Ltd. 2 Acetochlor·atrazine Suspension emulsion Tianjin Huayu Pesticide Co.， Ltd. 3 Clethodim Emulsion oil Jilin Jinqiu Agricultural Pharmaceutical Co.， Ltd. 4 Diquat Water-based solution Tianjin Huayu Pesticide Co.， Ltd. 5 2，4-D-ethylhexyl Emulsion oil Tianjin Huayu Pesticide Co.， Ltd. 6 Haloxyfop-P-methyl Emulsion oil Tianjin Huayu Pesticide Co.， Ltd. 7 Pendimethalin Emulsion oil Tianjin Huayu Pesticide Co.， Ltd.
Table 2. Samples of herbicides with gradient volume fractions
View tableTable 2. Samples of herbicides with gradient volume fractions
Group Treatment Description of sample Serial number of sample 1 Prepare herbicide solutions with volume fractions of 10%， 20%， 30%， 40%， 50%， 60%， 70%， 80%， 90%， and 100%，drip one drop （0.1 mL） of those solutions respectively onto the surface of the white paper fragments and then lay flat， dry in the shade for 24 h 10%‒100% volume fractions of herbicide 1 zctd1 10%‒100% volume fractions of herbicide 2 zytd2 10%‒100% volume fractions of herbicide 4 zdtd3 10%‒100% volume fractions of herbicide 6 zgtd4 10%‒100% volume fractions of herbicide 7 zetd5
Table 3. Samples of fabrics with herbicides
View tableTable 3. Samples of fabrics with herbicides
Group Treatment Name of fabric Number of herbicide Serial number of sample 2 Drip one drop （0.1 mL） of herbicide onto the surface of the fabric fragments and then lay flat， dry in the shade for 24 h Towel Herbicide 1 mc6 Herbicide 4 md7 Herbicide 5 mz8 Herbicide 6 mg9 Herbicide 7 me10 Pants Herbicide 1 yc11 Herbicide 4 yd12 Herbicide 5 yz13 Herbicide 6 yg14 Herbicide 7 ye15 Mask Herbicide 1 kc16 Herbicide 4 kd17 Herbicide 5 kz18 Herbicide 6 kg19 Herbicide 7 ke20 T-shirt Herbicide 1 bc21 Herbicide 4 bd22 Herbicide 5 bz23 Herbicide 6 bg24 Herbicide 7 be25 Socks Herbicide 1 wc26 Herbicide 4 wd27 Herbicide 5 wz28 Herbicide 6 wg29 Herbicide 7 we30
Table 4. Samples of corn kernels with herbicides
View tableTable 4. Samples of corn kernels with herbicides
Group Treatment Description of corn kernels Number of herbicide Serial number of sample 3 Soak the corn kernels in herbicide and mix thoroughly， then remove them out and lay flat， dry in the shade for 24 h Fresh Herbicide 4 freshd31 4 Dried Herbicide 1 dryc32 Herbicide 3 dryx33 Herbicide 4 dryd34 Herbicide 5 dryz35 Herbicide 6 dryg36
Table 5. Test method and duration
View tableTable 5. Test method and duration
Group Test method Imaging resolution /mm Duration /min 1 Reflection mode， with scan window of 160 ps 0.1 1020 2 Reflection mode， with scan window of 700 ps 750 3 Reflection mode， with scan window of 700 ps 120 4 Reflection mode， with scan window of 700 ps 600
Table 6. Imaging results of samples of group 2
View tableTable 6. Imaging results of samples of group 2
Herbicide Fabric substrate Result through natural light Result of terahertz imaging Glyphosate Towel Relatively clear Clear Pants Clear Clear Mask Clear Clear T-shirt None Clear Socks None Clear Diquat Towel Relatively clear Clear Pants Clear Clear Mask Relatively clear Clear T-shirt None Clear Socks None Clear 2，4-D-ethylhexyl Towel None Blurry Pants Blurry Blurry Mask None Relatively clear T-shirt None Blurry Socks None Relatively clear Haloxyfop-P-methyl Towel None None Pants Blurry Blurry Mask None Relatively clear T-shirt None Blurry Socks None Blurry Pendimethalin Towel Relatively clear Blurry Pants Clear Relatively clear Mask Clear Relatively clear T-shirt None Relatively clear Socks None Relatively clear
Table 7. Gray values of the background in terahertz images of group 2
View tableTable 7. Gray values of the background in terahertz images of group 2
Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 142 140 145 145 148 146 199 202 203 216 217 215 123 119 112 0‒0.5 THz 107 109 103 123 123 129 153 150 152 155 154 145 99 92 88 0.5‒1.5 THz 131 132 127 181 184 183 171 171 170 164 165 162 129 149 139 Diquat Time-domain spectral 162 158 166 82 80 82 175 182 177 195 187 191 120 130 145 0‒0.5 THz 197 174 175 69 77 73 152 139 132 181 202 183 128 162 151 0.5‒1.5 THz 232 204 193 116 102 111 195 199 182 198 199 195 194 197 180 2，4-D-ethylhexyl Time-domain spectral 124 140 138 140 135 143 114 147 151 198 201 210 135 130 133 0‒0.5 THz 159 166 170 148 141 139 233 193 120 254 252 252 205 215 203 0.5‒1.5 THz 125 131 140 140 137 134 117 130 146 185 179 186 195 188 206 Haloxyfop-P-methyl Time-domain spectral 190 181 178 231 210 209 167 131 175 194 200 191 201 189 192 0‒0.5 THz 152 152 136 179 185 211 151 255 191 136 156 135 158 153 148 0.5‒1.5 THz 140 151 137 168 176 174 178 212 161 157 155 152 163 161 164 Pendimethalin Time-domain spectral 134 121 127 154 157 150 172 181 175 183 198 188 227 228 253 0‒0.5 THz 139 150 123 196 215 190 113 153 102 242 220 199 145 149 147 0.5‒1.5 THz 161 106 136 224 186 212 138 139 151 198 201 200 118 113 119
Table 8. Mean gray values
of the background B in terahertz images of group 2 View tableTable 8. Mean gray values
of the background B in terahertz images of group 2 Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 142 146 201 216 118 0‒0.5 THz 106 125 152 151 93 0.5‒1.5 THz 130 183 171 164 139 Diquat Time-domain spectral 162 81 178 191 132 0‒0.5 THz 182 73 141 189 147 0.5-1.5 THz 210 110 192 197 190 2，4-D-ethylhexyl Time-domain spectral 134 139 137 203 133 0‒0.5 THz 165 143 182 253 208 2，4-D-ethylhexyl 0.5‒1.5 THz 132 137 131 183 196 Haloxyfop-P-methyl Time-domain spectral 183 217 158 195 194 0‒0.5 THz 147 192 199 142 153 0.5‒1.5 THz 143 173 184 155 163 Pendimethalin Time-domain spectral 127 154 176 190 236 0‒0.5 THz 137 200 123 220 147 0.5‒1.5 THz 134 207 143 200 117
Table 9. Gray values of the stain in terahertz images of group 2
View tableTable 9. Gray values of the stain in terahertz images of group 2
Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 51 53 46 30 34 33 68 86 67 94 89 73 26 28 20 0‒0.5 THz 15 9 22 4 1 8 24 32 79 67 50 63 7 0 1 0.5‒1.5 THz 0 7 0 1 2 3 5 26 38 52 0 19 0 53 30 Diquat Time-domain spectral 60 87 91 42 29 31 21 69 50 117 109 126 76 49 70 0‒0.5 THz 77 103 79 8 33 3 1 7 28 126 115 123 72 16 60 0.5‒1.5 THz 0 75 63 2 8 35 0 91 35 120 123 126 102 39 59 2，4-D-ethylhexyl Time-domain spectral 68 86 100 119 113 115 84 80 89 186 194 195 102 105 101 0‒0.5 THz 81 99 101 125 133 155 81 85 82 224 226 207 154 142 168 0.5‒1.5 THz 52 53 89 106 105 107 65 80 50 169 150 159 133 130 136 Haloxyfop-P-methyl Time-domain spectral 179 162 166 193 187 200 93 144 101 170 155 176 140 129 139 0‒0.5 THz 97 115 117 156 145 172 49 83 102 108 128 133 126 125 127 0.5‒1.5 THz 102 88 96 146 136 138 86 117 129 141 145 142 116 117 1321 Pendimethalin Time-domain spectral 106 105 104 142 136 136 90 116 119 168 146 178 174 170 169 0‒0.5 THz 95 93 119 192 164 188 42 21 59 179 178 186 131 138 139 0.5‒1.5 THz 19 0 5 136 96 102 30 55 57 171 175 173 90 99 95
Table 10. Mean gray values of the stain G in terahertz images of group 2
View tableTable 10. Mean gray values of the stain G in terahertz images of group 2
Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 50 32 74 85 25 0‒0.5 THz 15 4 45 60 3 0.5‒1.5 THz 2 2 23 24 28 Diquat Time-domain spectral 79 34 47 117 65 0‒0.5 THz 86 15 12 121 49 0.5‒1.5 THz 46 15 42 123 67 2，4-D-ethylhexyl Time-domain spectral 85 116 84 192 103 0‒0.5 THz 94 138 83 219 155 0.5‒1.5 THz 65 106 65 159 133 Haloxyfop-P-methyl Time-domain spectral 169 193 113 167 136 0‒0.5 THz 110 158 78 123 126 0.5‒1.5 THz 95 140 111 143 122 Pendimethalin Time-domain spectral 105 138 108 164 171 0‒0.5 THz 102 181 41 181 136 0.5‒1.5 THz 8 111 47 173 95
Table 11. |B-G| values of the terahertz images of group 2
View tableTable 11. |B-G| values of the terahertz images of group 2
Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 92 114 127 131 93 0‒0.5 THz 91 121 107 91 90 0.5‒1.5 THz 128 181 148 140 111 Diquat Time-domain spectral 83 47 131 74 67 0‒0.5 THz 96 58 129 67 98 0.5-1.5 THz 164 95 150 74 124 2，4-D-ethylhexyl Time-domain spectral 49 24 53 11 30 0‒0.5 THz 71 5 99 34 53 0.5‒1.5 THz 67 31 66 24 63 Haloxyfop-P-methyl Time-domain spectral 14 23 45 28 58 0‒0.5 THz 37 34 121 19 27 0.5‒1.5 THz 47 33 73 12 41 Pendimethalin Time-domain spectral 22 16 68 26 65 0‒0.5 THz 35 19 82 39 11 0.5‒1.5 THz 126 96 95 27 22
Table 12. Contrast values of the terahertz images of group 2
View tableTable 12. Contrast values of the terahertz images of group 2
Herbicide Kind of terahertz imaging Towel Pants Mask T-shirt Socks Glyphosate Time-domain spectral 73.59 75.46 75.73 74.60 75.16 0‒0.5 THz 74.44 78.26 77.32 75.17 85.15 0.5‒1.5 THz 85.99 80.62 81.98 83.18 77.16 Diquat Time-domain spectral 74.23 74.44 74.18 73.41 74.04 0‒0.5 THz 73.92 74.94 76.00 73.52 73.85 0.5‒1.5 THz 75.03 76.82 76.23 74.83 75.40 2，4-D-ethylhexyl Time-domain spectral 73.12 74.47 73.55 73.43 74.95 0‒0.5 THz 73.61 73.80 75.25 82.24 74.10 0.5‒1.5 THz 73.38 76.35 74.18 74.07 76.07 Haloxyfop-P-methyl Time-domain spectral 73.12 73.48 73.62 73.43 73.67 0‒0.5 THz 73.67 73.49 74.90 73.51 73.40 0.5‒1.5 THz 73.72 74.52 73.58 74.30 74.14 Pendimethalin Time-domain spectral 74.21 74.43 73.94 73.67 74.78 0‒0.5 THz 73.56 73.63 73.84 73.62 73.62 0.5‒1.5 THz 76.37 74.16 74.07 75.50 76.42
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Xinnuo Xu, Kaikai Li. Herbicide Stain Detection with Terahertz Imaging Combined with Image Enhancement[J]. Laser & Optoelectronics Progress, 2025, 62(16): 1630001
Paper Information
Category: Spectroscopy
Received: Jan. 6, 2025
Accepted: Mar. 5, 2025
Published Online: Aug. 6, 2025
The Author Email: Kaikai Li (zlkk77@163.com)
CSTR:32186.14.LOP250457
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