Comprehensive Study of Multiple CNNs Fusion for Fine-Grained Dog Breed Categorization

摘要

Fine-grained visual categorization aims to distinguish objects in subordinate classes instead of basic class, and is a challenge visual task due to the high correlation between subordinated classes and large intra-class variation (e.g. different object poses). Although, deep convolutional neural network (DCNN) has brought dramatic success on generic object classification, detection and segmentation with the availability of the large-scale training samples, direct application of DCNN on fine-grained visual categorization, where only decades or at most hundreds of training samples for each subordinate class are available in most public finegrained image datasets, cannot lead to satisfactory classification results due to small number of training samples. This study explores the transfer learning strategy for finegrained dog breed categorization based on the learned CNN models with the large-scale image dataset: ImageNet, and prove promising performance with two DCNN models: AlexNet and VGG-16. Furthermore, we argue that different DCNN architecture may extract the representation of different image aspects due to the previously defined CNN kernel sizes, number and various operations in the model learning procedure, and thus result in different performance for visual categorization. This study proposes to fusion multiple CNN architectures for combining different aspect representations to give more accurate performance. We compressively study the fusion of different layers such as Fc6 and Fc7 in AlexNet and VGG-16, and manifest 2.88% improvement of the fusion architecture over the best performance of the only one DCNN model: VGG-16 from 81.2% to 84.08%.