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China is the largest country for cultivating kiwifruit, and Shaanxi Province provides the largest production, which accounts for approximately 70% of the production in China and 33% of the global production. Harvesting kiwifruit in this region relies mainly on manual picking which is labor-intensive. Therefore, the introduction of robotic harvesting is highly desirable and suitable. The fast and effective recognition of kiwifruit in the field under natural scenes is one of the key technologies for robotic harvesting. Recently, the study on kiwifruit recognition has been limited to a single cluster and multi clusters in the field have seldom been considered. In this paper, according to growth characteristics of kiwifruit grown on sturdy support structures, an RGB (red, green, blue) camera was placed around 100 cm underneath the canopy so that kiwifruit clusters could be included in the images. We proposed a kiwifruit image recognition system based on the convolutional neural network (CNN), which has a good robustness avoiding the subjectivity and limitation of the features selection by artificial means. The CNN could be trained end to end, from raw pixels to ultimate categories, and we optimized the critical structure parameters and the training strategy. Ultimately, the network was made up of 1 input layer, 3 convolutional layers, 2 sub-sampling layers, 1 full convolutional layer, and 1 output layer. The CNN architecture was optimized by using batch normalization (BN) method, which normalized the data distribution of the middle layer and the output data, accelerating the training convergence and reducing the training time. Therefore, the BN layers were added after the 1, 3 and 5th convolutional layer (Conv1, Conv3, and Conv5 layer) of the original LeNet network. The size of all convolutional kernels was 5×5, and that of all the sub-sampling layers was 2×2. The feature map numbers of Conv1, Conv3, and Conv5 were 6, 16 and 120, respectively. After manual selection and normalizing, the RGB image of kiwifruit was transferred into a matrix with the size of 32×32 as the input of the network, stochastic gradient descent was used to train our models with mini-batch size of 100 examples, and momentum was set as 0.9. In addition, the CNN took advantages of the part connections, the weight sharing and Max pooling techniques to lower complexity and improve the training performance of the model simultaneously. The network used rectified linear units (ReLU) as activation function, which could greatly accelerate network convergence. The proposed model for training kiwifruit was represented as 32×32-6C-2S-16C-2S-120C-2. Finally, 100 images of kiwifruit in the field (including 5918 fruits) were used to test the model, and the results showed that the recognition ratios of occluded fruit, overlapped fruit, adjacent fruit and separated fruit were 78.97%, 83.11%, 91.01% and 94.78%, respectively. The overall recognition rate of the model reached 89.29%, and it only took 0.27 s in average to recognize a fruit. There was no overlap between the testing samples and the training samples, which indicated that the network had a high generalization performance, and the testing images were captured from 9 a.m. to 5 p.m., which indicated the network had a good robustness to lightness variations. However, some fruits were wrongly detected and undetected, which included the fruits occluded by branches or leaves, overlapped to each other and the ones under extremely strong sunlight. Particularly, 2 or more fruits overlapped were recognized as one fruit, which was the main reason to the success rate not very high. This phenomenon demands a further research. By comparing with the conventional methods, it suggested that the method proposed obtained a higher recognition rate and better speed, and especially it could simultaneously identify multi-cluster kiwifruit in the field, which provided significant support for multi-arm operation of harvesting robotic. It proves that the CNN has a great potential for recognition of fruits in the field. [ABSTRACT FROM AUTHOR]

Tea is one of important cash crops in China. Computer vision plays an important role in pest detection. Automatic classification of insect species in field is more difficult than the generic object classification because of complex background in filed and high appearance similarity among insect species. In this paper, we proposed an insect recognition system on the basis of image saliency analysis and a deep learning model, i.e. convolutional neural network (CNN), which has a good robustness with avoiding the features selected by artificial means. In image saliency analysis, we segmented the original images into super-pixel regions firstly. Then we quantized each RGB (red, green, blue) color channel and made them have 10 different values, which reduced the number of colors to 1000, and sped up the process of the color contrast of the pest objects and the background at region level. Finally, we obtained the saliency value of each region by combining their color contrast and spatial distances. The saliency values of all regions in each image were used to construct a saliency map, which was offered as the initial area for GrabCut algorithm to define the segmentation result and localize the pest object. The images after localization were quantized to 256×256 dpi for CNN training and classifying. CNN was trained end to end, from raw pixels to ultimate categories, thereby alleviating the requirement to manually design a suitable feature extractor. Based on theoretical analysis and experimental evaluation, we optimized the critical structure parameters and training strategy of CNN to seek the best configuration. The overall architecture included a number of sensitive parameters and optimization strategies that could be changed. We determined the local receptive field size, number, and convolutional stride as 7×7 dpi, 64 and 4, respectively. Dropout ratio for the fully-connected layers was 0.7. The loss function Softmax was fit for the pest classification system. To further improve the practical utility of CNN, we focused on structural changes of the overall architecture that enabled a faster running with small effects on the performance. We analyzed the performance and the corresponding runtime of our model by reducing its depth (number of layers) and width (number of convolution kernel in each layer). Removing the fully-connected layers (FC6, FC7) made only a slight difference to the overall architecture. These layers contained almost 90% of the parameters and when they were removed, the memory consumption decreased to 29.8 MB. But, removing the intermediate convolutional layers (Conv2, Conv3, Conv4, Conv5) resulted in a dramatic decrease in both accuracy and runtime. This suggested that the intermediate convolutional layers (Conv2, Conv3, Conv4, Conv5) constituted the main part of the computational resource, and their depth was important for achieving good results. We then investigated the effects of adjusting the sizes of all convolutional layers, and the filters in each convolutional layer were reduced to 64 each time. Surprisingly, all architectures showed significant decreases in running time with relatively small effects on performance. Finally, we determined the convolution kernel numbers of Conv2-5: 64-192-192-64. On the test set of tea field images, the architecture before and after shrinking respectively achieved the average accuracy (AA) of 0.915 and 0.881, respectively, superior to previous methods for pest image recognition. Further, after optimization the running time reduced to 0.7 ms and the memory required was 6 MB. [ABSTRACT FROM AUTHOR]