近年來，氣候變遷對於農業生產造成重大影響，如何維持農作物的產量儼然為農業領域上的一大課題。高溫以及降雨的改變使得植物的病害更為嚴重，而提前得知植物病害的發病狀況有助於避免病害擴散。由高光譜影像技術可以提前偵測到潛伏期的病徵，進而避免草莓炭疽病的蔓延。為了改善植物病害的辨識效率，本研究致力於建立一套手持式多光譜影像裝置以檢測植物病害。此裝置使用嵌入式系統當作系統的控制器，藉由放置於微型攝影機之前的濾鏡，可以擷取到所需要的特徵波段影像。藉由這些影像的資訊，可以得到不同波段的染病資訊。手持式多光譜裝置擷取四個波段的影像後，經過白校正影像處理以降低光線不均勻的影響後，藉由觀察接種炭疽病孢子液後的草莓葉片，由多光譜以及RGB影像資訊，可以分析不同時期的發病狀況。在本研究當中，我們首先以手持式多光譜裝置辨識草莓葉片的健康期以及病徵期兩種狀態，然後再進一步進行草莓葉片的健康期、潛伏期和病徵期三種狀態的辨識。在葉片平整的狀況下，本研究利用SVM模型在兩類病害分析上可以到達90.0%以上的準確率，而在三類病害分析上則可以在健康期、潛伏期以及染病期上面得到92.2%、68.6%和97.9%的準確率。染病草莓葉片以多光譜裝置取像後可以利用假彩色的方式呈現不同時期的病害症狀，讓使用者簡單且準確的得知染病植物的狀況，以採取適當防治措施。由於不平整葉片上的陰影會嚴重影響多光譜影像裝置的病害分析辨識率，因此我們進一步提出一個透過影像組合的方法來降低陰影所造成辨識率降低的影響。經過觀察多光譜影像彼此之間的關聯後，建立了四個較具有判別陰影、病徵以及健康區域的組合影像。以新的組合影像進行SVM訓練，健康期的辨識率由71.3%提高到95.7%，而病徵期的辨識率由82.3%提高到88.9%。In recent years, the climate change has significantly affected the agricultural production. Maintaining the crop production is one of main concerns in agriculture. High temperature and changes of rainfall patterns enhance the spread of plant diseases. Hence it is desirable to seek for early detection of plant disease, and thus to control the spread of plant disease. Hyperspectral imaging has been proved to be an efficient tool for early detection of strawberry Anthracnose. To improve the efficiency of plant disease detection, this research aims to build a handheld multispectral imaging device for strawberry Anthracnose detection. This device uses an embedded system as the controller of the device. By placing filters in front of four miniature cameras, the images of four characteristic wavelengths are acquired. After capturing images using the handheld multispectral imaging device, images are processed to correct the effect of uneven lighting. Then by further processing the multispectral images and incorporating the RGB image of inoculated strawberry leaves, we are able to analyze the status of strawberry leaves at various infection stages. In this research, we first used the multispectral imaging device to classify the healthy and symptomatic areas in strawberry leaves. Then we further attempted to classify the status into three categories: healthy, incubation and symptomatic. SVM model was applied for classification of infection stages. For classification of healthy and symptomatic status, detection accuracy is above 90%. For classification between healthy, incubation, and symptomatic status, the accuracies are 92.2%, 68.6%, and 97.9%, respectively. The classification result of strawberry Anthracnose infection is further displayed on the handheld device as pseudo-color image so the user can easily observe the plant health condition, and so the disease management can be applied if necessary. Since the detection accuracy can be affected by lighting and shadow due to uneven surface of strawberry leaves. We propose a method to amend the effect of shadow on status classification. Through observations of the original four images and their association, a new set of images derived from the original four images was selected and tested to rectify the shadow effect. Using this new set of derived images and trained with SVM, classification accuracy for healthy status increased from 71.3% to 95.7% and the classification accuracy for symptomatic status also increased from 82.3% to 88.9%
