As Huawei P30 Pro could make such vivid pictures

Huawei P30 Pro is the first smartphone that uses the new Sony sensor IMX650. In addition to resolution 40 megapixels feature of this sensor is in the fact that it has a color filter RYYB. Huawei claims that this new sensor is capable of collecting up to 40%. But what is color filter RYYB and how it differs from those installed in other smartphones?

To understand the operation of the filter RYYB, we must first understand how the Bayer filter. The Bayer filter is a color filter array superimposed over the image sensor, and is named after Bryce Bayer, who invented it.

The reason we need an array of color filters, is that the image sensor by design is sensitive only to light and not sensitive to color. Because it can detect and track only light a raw image from a digital image sensor always black and white.

To be able to fix the color, we need an array of color filters such as a Bayer filter. First, the ultraviolet and infrared radiation is filtered out by other filters. As soon as a light is narrowed to the visible spectrum, the filter Bayer starts to work.

The Bayer filter imposes one coloured dye over each pixel. Thus, in the grid of size 2×2 pixel is one red pixel, one blue pixel and two green pixels.

To use the RGB filter is reasons. Human vision trichromatic, which means that it is sensitive primarily to the three groups of light waves that are close in correspondence to the red, green and blue colors. Using the overlap between these wavelengths, our brain is able to interpret the “color” (which actually does not exist) and along with the light information collected by the retina of our eyes, we can see. Our cameras are designed to mimic our system trichromatism of view.

The Bayer filter places one red, one blue and two green lenses on the pixel grid of 2×2 on the image sensor. This means that visible light passing through the array, filtered with the corresponding color. A pixel under a red lens will still get a black and white image, but with a filtered red. This will cause all the red objects in the frame will seem brighter for this pixel as the removal of this information. The same applies to blue and green pixels.

Now we have the image because of the filters has different levels of brightness for each pixel. To get the true colors, we need a process called demosaicing or post-Bayer linearization. A complex algorithm is usually owned by the manufacturer of the camera that helps to interpret the different meanings of color. It scans the information captured by the pixel and the surrounding pixels and determines what color value to assign to this pixel. The quality of this algorithm determines how accurate are the colors on the final image.

In addition, a raw digital image from the sensor always black and white. We see color only because the image has been processed by the algorithm post-Bayer linearization. When we open the raw file format RAW photo editor such as Adobe Photoshop, the app uses its own algorithm to generate demosaicing colors, so different apps will create a bit of a different color for RAW files.

Once the process of demosaicing completed, the image is ready for further processing, where such things as exposure, contrast, shadows, white balance, noise and sharpness are adjusted to produce the final image.

Returning to the filters, the filter uses a Bayer RGGB array. As mentioned earlier, it most closely matches the way our eyes work. As for why exactly the green pixel is two pieces, it’s because green is in the centre of the visible colors, and our eyes are most sensitive to it. The green channel also acts as a brightness, and you can see that the adjustment of the amount of green in the image affects not only the color but also in the overall brightness of the image.

However, the Bayer filter there are alternatives. CYM or CYYM is one of them, and here the filter consists of cyan, yellow and Magenta colors. The advantage of the filter CYYM is that it allows more light to pass to the sensor. As the name implies, the Bayer filter is a filter, so it filters or removes some of the light. Furthermore, since only half of the pixels on the sensor gets the green light, and a quarter is red and blue, you will never be able to promise this sensor resolution. Sensor CYYM with its higher degree of light transmission was developed to circumvent the complex patterns and is theoretically able to provide much greater resolution for the same number of pixels.

However, as it turns out, to obtain a natural image from the sensor CYYM not easy, and it requires a much more complex algorithm demosaicing than RGGB. Because of this, he never gained popularity, and camera filter CYYM remain rare, and in the recent past, they were not at all in the market.

Here comes to the aid of the sensor of the P30 RYYB Huawei Pro. Engineers used the familiar red and blue channels, but was replaced by two green two yellow channel. This allows the sensor to capture more light than with the green filters, at least in theory.

Of course, there is still the problem of demosaicing, but progress in this area, as well as using artificial intelligence that analyzes image content, it is now possible to correctly identify colors, even without a dedicated green channel.

Of course, the effectiveness of this method compared with the standard RGGB cannot be easily tested or proven, so long as we only believe Huawei’s word for it. But it is certainly an interesting solution to improve image quality in poor light conditions and perhaps the reason why Chinese smartphone capable of delivering such impressive photos in low light.

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