Handheld Multi-Frame Super-Resolution
"Handheld Multi-Frame Super-Resolution", B. Wronski, I. Garcia-Dorado, M. Ernst, D. Kelly, M. Krainin, C.K. Liang, M. Levoy, and P. Milanfar*, in ACM Transactions on Graphics, Vol. 38, No. 4, Article 28, July 2019 (SIGGRAPH 2019)
Compared to DSLR cameras, smartphone cameras have smaller sensors, which limits their spatial resolution; smaller apertures, which limits their light gathering ability; and smaller pixels, which reduces their signal-to-noise ratio. The use of color filter arrays (CFAs) requires demosaicing, which further degrades resolution. In this paper, we supplant the use of traditional demosaicing in single-frame and burst photography pipelines with a multi-frame super-resolution algorithm that creates a complete RGB image directly from a burst of CFA raw images. We harness natural hand tremor, typical in handheld photography, to acquire a burst of raw frames with small offsets. These frames are then aligned and merged to form a single image with red, green, and blue values at every pixel site. This approach, which includes no explicit demosaicing step, serves to both increase image resolution and boost signal to noise ratio. Our algorithm is robust to challenging scene conditions: local motion, occlusion, or scene changes. It runs at 100 milliseconds per 12-megapixel RAW input burst frame on mass-produced mobile phones. Specifically, the algorithm is the basis of the Super-Res Zoom feature, as well as the default merge method in Night Sight mode (whether zooming or not) on Google’s flagship phone.
We gratefully acknowledge current and former colleagues from collaborating teams across Google including: Haomiao Jiang, Jiawen Chen, Yael Pritch, James Chen, Sung-Fang Tsai, Daniel Vlasic, Pascal Getreuer, Dillon Sharlet, Ce Liu, Bill Freeman, Lun-Cheng Chu, Michael Milne, and Andrew Radin. Integration of our algorithm with the Google Camera App as Super-Res Zoom and Night Sight mode was facilitated with generous help from the Android camera team. We also thank the anonymous reviewers for valuable feedback that has improved our manuscript.
