Google HDR+ Image Processing Pipeline

Introduction

HDR Overview High dynamic range, or HDR is a image processing technique which allows photographers to create vibrant images with color contrasts which are more representative of what is seen by the human eye. Traditional HDR methods utilize a technique called exposure bracketing where images are taken at different exposures (one under exposed, one at normal exposure, and the last over exposed) and the best parts of each are used to produced the final image. Typically, under exposed images will capture the bright areas of a scene the best, while over exposed images will capture the darker parts of the scene the best. Specifically, parts of each exposure are chosen such that features of the bright and dimmer areas of the photo are visible and clear.

HDR+ Pipeline While the exposure bracketing works well in capturing HDR images on professional photography, it is not suitable for mobile photography, where computation resource is limited and the post processing pipeline is highly automated. To address the issue, Google AI presented a new pipeline, HDR+, for Google’s Pixel phone using constant exposure and new alignment and merging algorithms. In HDR+, the frames are captured with low enough exposure to avoid blowing out the highlights; the pipeline begins at Bayer raw frames rather than the demosaicked RGB frames[1].

Appendix

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