Ever since Google dropped its Nexus line-up and released Pixel devices, one of the main features of the series is the camera performance and software used in image processing. The Google Pixel 5 and the Pixel 4a 5G improves on the same, with the company using an ultrawide lens on both devices.
But it’s not just the hardware alone, as Google has proved in the past. Software optimizations and image processing algorithms weigh in as much. Google recently upgraded the Pixel 5 and the 4a 5G variant with HDR+ bracketing technology.
At the company’s Launch Night in its keynote, Google said that “exposure bracketing” is a pretty significant upgrade to the existing HDR+ and stated that it mixed innovative Google techniques with traditional HDR image capturing algorithm.
According to the Mountain View-based company, the HDR+ burst photography system, which underexposed images so as to prevent loss of detail, often results in noisy shadows when it comes to high dynamic range scenes.
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.
Till now, the approach to the problem involved combining two images with different exposures, but it proved to be complex since it requires the camera to capture more long exposure frames while retaining the Pixel’s quick capture experience.
Another thing to take into consideration is that the camera needs to make full use of the long exposure all the while avoiding the ghosting effect that quick motion causes between several frames.
Google had to completely redesign how Pixel devices capture images in a burst while maintaining the zero shutter lag.
For bracketing, we capture an additional long exposure frame after the shutter press, which is not shown in the viewfinder. Note that holding the camera still for half a second after the shutter press to accommodate the long exposure can help improve image quality, even with a typical amount of handshake.
However, the problem does not persist in Night Sight and it is one of the reasons why Google was able to work with exposure bracketing on the Pixel 4 and the Pixel 4a.
The Pixel 4a and the Pixel 5 are able to work with HDR+ with bracketing on the default camera as well as Portrait mode.
No user interaction is needed to activate HDR+ with Bracketing — depending on the dynamic range of the scene, and the presence of motion, HDR+ with bracketing chooses the best exposures to maximize image quality (examples).
Left: The result of merging 12 short-exposure frames in Night Sight mode. Right: A single frame whose exposure time is 12 times longer than an individual short exposure. The longer exposure has significantly less noise in the shadows but sacrifices the highlights.
The addition of the bracketing technique on HDR+ images definitely improves the overall image detail which was lost using traditional techniques.