The Honor V9 features a third-generation 12MP f/2.2 dual camera at the back of the phone. One sensor is an RGB sensor that captures the color data, like any conventional Bayer sensor. The second sensor is a monochrome sensor that captures three times the amount of light, but it's a monochrome one. The reason for the better light gathering capability is due to the fact that there are not colors filters above the micro-lenses, so each pixel captures more light photons.
The dual-lens camera setup has two main uses: one, to improve the low-light performance and image quality of photos, and second, to help take photos with very shallow depth of field effect. Until the multiple-layer sensor technology arrives, a dual-lens camera setup is the best option we have to achieve a significantly better low light performance, as well as providing users with the ability to produce DSLR-like blur background effect. The f/2.2 aperture is relatively slow if you compare it to the other lenses that we've seen on other flagship smartphones. Having said that, the main reason I personally want a fast aperture lens is for two reasons: one, to get better low-light performance and second, to be able to achieve a more prominent background blur effect. With the dual-lens camera setup, I can achieve both, and even much better Bokeh effect compared to a single-lens camera setup, so not too many complain here.
Just a reminder, the Hono V8 also camera with dual 12MP f/2.2 cameras. The good news is that Huawei has chosen to stay with a 12MP sensor and not go with a higher resolution. Those sensors have 1.25 µm pixels. We've seen phones like the Google Pixel that comes with a 12.3MP sensor but has 1.55-micron pixels. This suggests that the sensor in the Honor V9 are smaller, thus the pixel size is smaller as well. I can understand that putting larger sensor will affect its price or because there is just a limited amount of space to put larger sensors. Another thing is that maybe the black and white sensor needs to have the same properties as the color one, and therefore the Bayer sensor needed to match the monochrome sensors which are at a particular size. Whatever the reason, the color reproduction should be really very good, with very good image details and decent low-light performance. I was pleased with the V8 dual-lens camera performance. The dual-lens camera allows people to take higher-quality photos and with much more expressive and prominent shallow depth of field effect, the same one that you can achieve with a digital SLR camera and a fast prime lens.
This dual-lens camera setup is definitely one of the main key selling features of the Huawei Honor V9. By the way, I don't know how dual-lens camera with a B&W sensor is compared to a single camera with a faster aperture lens, it would be nice if there was such a comparison, so we can know in numbers how effective this setup is compared to a camera with a single sensor and a faster lens/