HDR+ with Bracketing on Pixel Phones

Posted by Manfred Ernst and Bartlomiej Wronski, Software Engineers, Google Research

We’re continuously working to improve the Pixel — making it more helpful, more capable, and more fun — with regular updates, such as the recent V8.2 update to the Camera app. One such improvement (launched on Pixel 5 and Pixel 4a 5G in October) is a feature that operates “under the hood”, HDR+ with Bracketing. This feature works by merging images taken with different exposure times to improve image quality (especially in shadows), resulting in more natural colors, improved details and texture, and reduced noise.

Why Are HDR Scenes Hard to Capture?
The original HDR+ burst photography system is the engine behind high-quality mobile photography, which captures a rapid series of deliberately underexposed images, then combines and renders them in a way that preserves detail across the range of tones. But this system had one limitation: scenes with high dynamic range (HDR) like the one below were noisy in the shadows because all images captured are underexposed.

The same photo using HDR+ (red outline) and HDR+ with Bracketing (green outline). While the characteristic HDR+ look remains the same, bracketing improves image quality, especially in shadows, with more natural colors, improved details and texture, and reduced noise.

Capturing HDR scenes is difficult because of the physical constraints of image sensors combined with limited signal in the shadows. We can correctly expose either the shadows or the highlights, but not both at the same time.

The same scene shot with different exposure settings and tonemapped to similar overall brightness. Left/Top: Exposure set for the highlights. The bright blue sky is preserved, but the shadows are very noisy. Right/Bottom: Exposure set for the shadows. Noise in the shadows is reduced, but the sky is clipped (white).

Photographers sometimes work around these limitations by taking two different exposures and combining them. This approach, known as

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