5.3 A Data-Compressive 1.5b/2.75b Log-Gradient QVGA Image Sensor with Multi-Scale Readout for Always-On Object Detection. Young, C., Omid-Zohoor, A., Lajevardi, P., & Murmann, B. In 2019 IEEE International Solid- State Circuits Conference - (ISSCC), pages 98–100, February, 2019.
doi  abstract   bibtex   
Histograms of Oriented Gradients (HOG) are attractive features for object detection in embedded vision applications, as they provide a good trade-off between complexity and detection accuracy. A custom 8b CMOS imager that computes these features on-chip consumes only 52pJ/pixel [1]. However, a complete system also requires a backend detection algorithm, which consumes 940pJ/pixel in an optimized implementation [2]. As shown in the system study of [3], this imbalance mostly stems from the large amount of data seen by the detector. To remedy this issue, the work of [3] studies a feature-extraction approach that aggressively log-quantizes the data, thereby eliminating unnecessary illumination-related bits from the histograms. The custom log-gradient image sensor described in this paper demonstrates this concept in CMOS. It consumes 127pJ/pixel and offers two log-gradient modes (1.5b and 2.75b) along with multi-scale readout. With several algorithmic enhancements enabled by the log gradients as described in [3], the resulting HOG feature compression ratios are 25× (1.5b) and 9.5× (2.75b) when compared to a standard 8b image (without image pyramid). Using 1.5b log gradients, [3] conservatively estimates a 3.3× reduction in backend detection energy for a deformable parts model (DPM) based detector.
@inproceedings{young_5.3_2019,
	title = {5.3 {A} {Data}-{Compressive} 1.5b/2.75b {Log}-{Gradient} {QVGA} {Image} {Sensor} with {Multi}-{Scale} {Readout} for {Always}-{On} {Object} {Detection}},
	doi = {10.1109/ISSCC.2019.8662436},
	abstract = {Histograms of Oriented Gradients (HOG) are attractive features for object detection in embedded vision applications, as they provide a good trade-off between complexity and detection accuracy. A custom 8b CMOS imager that computes these features on-chip consumes only 52pJ/pixel [1]. However, a complete system also requires a backend detection algorithm, which consumes 940pJ/pixel in an optimized implementation [2]. As shown in the system study of [3], this imbalance mostly stems from the large amount of data seen by the detector. To remedy this issue, the work of [3] studies a feature-extraction approach that aggressively log-quantizes the data, thereby eliminating unnecessary illumination-related bits from the histograms. The custom log-gradient image sensor described in this paper demonstrates this concept in CMOS. It consumes 127pJ/pixel and offers two log-gradient modes (1.5b and 2.75b) along with multi-scale readout. With several algorithmic enhancements enabled by the log gradients as described in [3], the resulting HOG feature compression ratios are 25× (1.5b) and 9.5× (2.75b) when compared to a standard 8b image (without image pyramid). Using 1.5b log gradients, [3] conservatively estimates a 3.3× reduction in backend detection energy for a deformable parts model (DPM) based detector.},
	booktitle = {2019 {IEEE} {International} {Solid}- {State} {Circuits} {Conference} - ({ISSCC})},
	author = {Young, C. and Omid-Zohoor, A. and Lajevardi, P. and Murmann, B.},
	month = feb,
	year = {2019},
	pages = {98--100}
}

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