The last 10 years have seen a seesaw of emphasis between more pixels and bigger pixels in phone cameras. First, resolution gets pushed to the limits by using increasingly small pixels crammed onto the necessarily tiny sensors. Then there’s a backlash from those who value low-light performance and low noise that pushes vendors to use larger pixels, lowering overall resolution.
Sony is the latest firm to try and offer a chip that accommodates both use cases. Its new IMX586 is officially a 48MP imaging sensor, but by using a Quad Bayer pixel layout, it has a straightforward way to bin each group of four adjacent pixels to create 12MP images that should have similarly low noise as a native 12MP sensor.
Quad Bayer, and How It Works
Almost all consumer camera sensors made today, like Sony’s Xperia ZX2 (pictured on top), use the tried-and-true Bayer array. Rows of Red and Green alternate with rows of Green and Blue. The result is a preference for green (the middle of the visible spectrum, and the region to which our eyes are the most sensitive), but with enough Red and Blue that through de-mosaicing a complete RGB image can be formed.
Quad Bayer is the same principle, but each pixel is really 4 smaller pixels. So the rows look like Red-Red Green-Green, Red-Red Green-Green, Red-Red Green-Green, Green-Green Blue-Blue, and Green-Green Blue-Blue.
Two clever pieces of technology are needed to make this work. The first is a new de-mosaicing algorithm that can synthesize RGB at all 48 million photosites, even though some are more than a pixel away from one of those colors. It’ll be interesting to see how well Sony and the smartphone makers it sells to will do on that score. The second is a binning readout option that groups adjacent pixels together for a 12MP image. Here too we’ll have to see how combining four .8 micron pixels compares with the native readout from a native 12MP sensor’s 1.6-micron pixel image. Not surprisingly, Sony claims it will be comparable.
Sony IMX586 By the Numbers
As smartphone sensors go, the 1/2-inch format (6.4 x 4.8 mm) of the stacked CMOS IMX586 makes it relatively large. Many phones use a smaller 1/3-inch format sensor. As you’d expect, its typical operation will use the full 48MP in bright light and fall back to 12MP in low light. Sony also appears to have an additional mode of operation, where it can switch some of the pixels off mid-exposure. That allows for native HDR capture, like that pioneered by startup Pixim, whose assets were acquired by Sony several years ago. Sony claims that as a result, the IMX586 can capture four times more dynamic range than previous versions.
One other interesting feature of the chip is that it can capture 4K video at 90fps, and 1080p video at 240fps. It also comes with Phase-difference Autofocus. Sony expects to start sampling the IMX586 in September, with a sample price of about $27.
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