Google explains how the Pixel 4’s Astrophotography works and shares tips on how to take them

Even before Google launched the Pixel 4 series, its Astrophotography mode caught the attention of users worldwide. The new enhanced night-mode setting in the Google Camera app allowed users to capture amazing photos of the starry night sky. However, capturing photos like the ones you might have seen on social media isn’t as easy as it may seem. There are several parameters you need to keep in mind to capture a decent shot, which is why Google has now released some much-needed insight about the new feature.

In a recent blog post titled ‘Astrophotography with Night Sight on Pixel Phones’, Google’s Florian Kainz and Kiran Murthy explain how the new mode came about. The post talks about the company’s inner workings and reveals key details about how the engineers fixed the exposure times for each frame and the number of frames to capture to achieve the best results while avoiding any motion blur.

Motion-blurred stars in a single-frame two-minute exposure.

Then it sheds light on how the company tackled issues with Dark current, which causes CMOS image sensors to record incorrect signals that result in individual pixels lighting up even when they’re not exposed to as much light. To combat this issue, the company compared the values of neighboring pixels within the same frame and across the sequence of frames to look for outliers. It then eliminated these outliers by concealing it with the average value of its neighbors.

Left: A small region of a long-exposure image with hot pixels, and warm pixels caused by dark current nonuniformity. Right: The same image after outliers have been removed. Fine details in the landscape, including small points of light, are preserved.

Google then talks about scene composition and how they had to display a “post-shutter viewfinder” in Night Sight in order to help users see what they were shooting. Without this implementation, you’d mostly see a gray screen which makes composing the shot quite difficult. Autofocus was another issue that the company faced due to a similar reason and in order to resolve that it implemented “post-shutter autofocus”. This new feature captured two autofocus frames with exposure times up to one second to help detect image details even in low light. These frames helped the Pixel 4’s camera focus properly on the subject but didn’t contribute directly to the final image.

Left: The live Night Sight viewfinder in a very dark outdoor environment. Except for a few points of light from distant buildings, the landscape and the sky are largely invisible. Right: The post-shutter viewfinder during a long exposure shot. The image is much clearer; it updates after every long-exposure frame.

Finally, Google had to change how it processed the sky in Night Sight photos to deliver believable results. The processing not only helped make the sky look darker, as you’d expect it to look at night, but also added sky-specific noise reduction and selectively increased contrast to make certain features more prominent.

A landscape picture taken on a bright full-moon night, without sky processing (left half), and with sky darkening (right half). Note that the landscape is not darkened.

During the course of developing and testing Night Sight astrophotography, Google’s engineers also gained some experience taking outdoor night time pictures. And in order to help you capture better Night Sight photos with your Pixel device (or any phone with the GCam mod), the company has shared a list of tips and tricks. You can find the tips and tricks by following this link and improve the quality of your Night Sight astrophotography images significantly. You can follow the link below for more detailed info on how the Pixel 4’s astrophotography feature works.

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Source: Google Blog

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