  The need for large annotated image datasets for training Convolutional Neural
Networks (CNNs) has been a significant impediment for their adoption in
computer vision applications. We show that with transfer learning an effective
object detector can be trained almost entirely on synthetically rendered
datasets. We apply this strategy for detecting pack- aged food products
clustered in refrigerator scenes. Our CNN trained only with 4000 synthetic
images achieves mean average precision (mAP) of 24 on a test set with 55
distinct products as objects of interest and 17 distractor objects. A further
increase of 12% in the mAP is obtained by adding only 400 real images to these
4000 synthetic images in the training set. A high degree of photorealism in the
synthetic images was not essential in achieving this performance. We analyze
factors like training data set size and 3D model dictionary size for their
influence on detection performance. Additionally, training strategies like
fine-tuning with selected layers and early stopping which affect transfer
learning from synthetic scenes to real scenes are explored. Training CNNs with
synthetic datasets is a novel application of high-performance computing and a
promising approach for object detection applications in domains where there is
a dearth of large annotated image data.
