Despite significant research on lightweight deep neural networks (DNNs) designed for edge devices, the current face detectors do not fully meet the requirements for "intelligent" CMOS image sensors (iCISs) integrated with embedded DNNs. These sensors are essential in various practical applications, such as energy-efficient mobile phones and surveillance systems with always-on capabilities. One noteworthy limitation is the absence of suitable face detectors for the always-on scenario, a crucial aspect of image sensor-level applications. These detectors must operate directly with sensor RAW data before the image signal processor (ISP) takes over. This gap poses a significant challenge in achieving optimal performance in such scenarios. Further research and development are necessary to bridge this gap and fully leverage the potential of iCIS applications. In this study, we aim to bridge the gap by exploring extremely low-bit lightweight face detectors, focusing on the always-on face detection scenario for mobile image sensor applications. To achieve this, our proposed model utilizes sensor-aware synthetic RAW inputs, simulating always-on face detection processed "before" the ISP chain. Our approach employs ternary (-1, 0, 1) weights for potential implementations in image sensors, resulting in a relatively simple network architecture with shallow layers and extremely low-bitwidth. Our method demonstrates reasonable face detection performance and excellent efficiency in simulation studies, offering promising possibilities for practical always-on face detectors in real-world applications.

翻译：尽管面向边缘设备设计的轻量级深度神经网络（DNN）已有大量研究，但当前的人脸检测器尚不能完全满足集成嵌入式DNN的"智能"CMOS图像传感器（iCIS）需求。此类传感器在能效优先的移动电话和具备常开功能的监控系统等实际应用中至关重要。一个显著局限在于缺乏适用于常开场景的专用检测器——这是图像传感器级应用的关键环节。该类检测器必须在图像信号处理器（ISP）接管之前直接处理传感器原始数据。这一空白对实现此类场景的最优性能构成重大挑战，亟需进一步研究来弥合差距并充分释放iCIS应用潜力。本研究旨在通过探索面向移动图像传感器常开人脸检测场景的极低位宽轻量级人脸检测器来填补这一空白。我们提出的模型采用传感器感知的合成RAW输入，模拟ISP链"前"处理的常开人脸检测流程。该方法通过三值（-1,0,1）权重适配图像传感器的潜在实现需求，构建了浅层架构与极低位宽相结合的相对简化网络结构。仿真研究表明，我们的方法在保持合理人脸检测性能的同时展现出卓越的能效，为实际应用中实现常开型人脸检测器提供了可行方案。