In this article we are going to understand "PatchNet: A Simple Face Anti-Spoofing Framework via Fine-Grained Patch Recognition". Fine Grained Patch-Type recognition problem: From each of cropped faces, they extract two equi-sized patches. Thus, no matter the differences in the image sizes, there is no need of image distortion. This helps in training the network as well, as in every epoch some new patches from the same face would be cropped acting as an additional augmentation along with random horizontal flip and random rotation. Asymmetric margin based softmax loss: Instead of using Cross-entropy, this loss allowed the authors to specify margin of separation between classification boundaries, thus reducing the chances of wrong classification.

Object recognition is a fundamental problem in many video processing tasks, accurately locating seen objects at low computation cost paves the way for on-device video recognition. We propose PatchNet, an efficient convolutional neural network to match objects in adjacent video frames. It learns the patchwise correlation features instead of pixel features. PatchNet is very compact, running at just 58MFLOPs, $5\times$ simpler than MobileNetV2. We demonstrate its application on two tasks, video object detection and visual object tracking. On ImageNet VID, PatchNet reduces the flops of R-FCN ResNet-101 by 5x and EfficientDet-D0 by 3.4x with less than 1% mAP loss. On OTB2015, PatchNet reduces SiamFC and SiamRPN by 2.5x with no accuracy loss. Experiments on Jetson Nano further demonstrate 2.8x to 4.3x speed-ups associated with flops reduction. Code is open sourced at https://github.com/RalphMao/PatchNet.

Biometrics emerged as a robust solution for security systems. However, given the widespread of biometric applications, criminals are developing techniques to circumvent them by simulating physical or behavioral traits of legal users (spoofing attacks). Despite face being a promising characteristic due to its universality, acceptability and presence of cameras almost everywhere, face recognition systems are extremely vulnerable to such frauds since they can be easily fooled with common printed facial photographs. State-of-the-art approaches, based on Convolutional Neural Networks (CNNs), present good results in face spoofing detection. However, these methods do not exploit the importance of learning deep local features from each facial region, even though it is known from face recognition that different face regions have much different visual aspects, that can also be exploited for face spoofing detection. In this work we propose a novel CNN architecture trained in two steps for such task. Initially, each part of the neural network learns features from a given facial region. After, the whole model is fine-tuned on the whole facial images. Results show that such pretraining step allows the CNN to learn different local spoofing cues, improving the performance and convergence speed of the final model, outperforming the state-of-the-art approaches.