How do multi-camera phones handle very close subjects?
Asked 8/26/2018
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Some phones combine data from two or more rear cameras into one photo for effects like lower noise or depth-based refocusing. But the lenses are spaced a few centimeters apart, so with nearby subjects the views can differ a lot because of parallax. How do these phones deal with close subjects when combining images? Do they still merge both cameras’ data, use parallax to build a depth map, or fall back to just one camera if the images don’t match well?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
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I don't own such a phone. However, based on sample images available online, some phones (such as the Samsung S9+) store images from both cameras in the same JPEG file. See How to extract depth information from JPEG files?
With the Google Camera app, when taking pictures that contain depth information, there is a tool to select a different focus point. There is likely something similar to select which image is the primary image. The specific interface is likely to vary by phone.
The secondary camera of some phones captures only grayscale images. At the minimum focusing distance of the cameras, the main subject should be visible in both cameras. Parallax may be used to calculate a depth map. If the images cannot be correlated with each other, the secondary image is likely simply ignored.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
8y ago
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At close distances, multi-camera phones usually don’t need to fully merge two mismatched views into one detailed image. Instead, they often use the second camera mainly for depth estimation or supplemental data.
Because the cameras are separated, nearby subjects produce noticeable parallax. That parallax can actually help the phone calculate a depth map for portrait effects or refocusing. Some phones even store depth-related information alongside the JPEG, and apps may let you change focus afterward.
In some designs, the secondary camera may capture only monochrome data, which can be used to support detail or noise performance when the views correlate well enough.
If the two images can’t be matched reliably—especially with very close subjects—the phone can simply rely more on the primary camera and ignore the secondary data. In practice, the main subject is usually still within both cameras’ minimum focusing range, so the system can often get at least useful depth information even if full image fusion is limited.
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