The main camera sits behind an f/1.8 lens, and takes 10-megapixel images by default, in a downsampled mode that allows it to shoot with an equivalent pixel size of 2 microns at that lower resolution. (A technique known as pixel binning turns a 40 megapixel sensor with 1-micron pixels into a 10-megapixel shooter with 2-micron pixels.) That's huge for low-light photography, as well as just being able to produce a high-quality image at 10 megapixels without fine detail becoming mushy. It's an ambitious camera setup to be sure, and to Huawei's credit, for the most part it works incredibly well.
AI magic on a 40-megapixel sensor helps the P20 Pro take stunning low-light shots, leapfrogging the Pixel 2.
Meanwhile, that monochrome sensor, behind an f/1.6 lens, is used to add in fine detail. And by combining this with the dedicated 3X telephoto camera, the P20 Pro can achieve 5X hybrid zoom. That gives you zoomed images with a unique field of view that really don't look like they were taken on a smartphone. Huawei's camera setup also sticks with the telephoto camera even in relatively dark conditions, unlike the Samsung Galaxy S9+, which quickly reverts back to a digital crop of the main sensor in even middling light. Generally that's a good thing, however the point at which the P20 Pro does switch to a digital crop of the 40-megapixel main sensor is highly noticeable, because a 3X digital crop is significantly grainier, even with that larger sensor size.
Regardless, 3X telephoto gives the Huawei P20 Pro a unique strength -- you can zoom further with more detail than any other phone camera.
But where the P20 series truly excels is in the handheld night mode. Both models have it, but that's strongest on the P20 Pro, thanks to that pixel-binning magic. In this mode, the phone shoots a series of exposures over around 4 seconds, then does some number-crunching, uses AI to counteract hand motion, and normally leaves you with a mind-blowingly awesome low-light photo. (It's not unlike the HDR+ "enhanced" mode from Google's Pixel 2 phones, only shot over a longer period of time.)
In full auto mode, the P20 Pro is pretty great at low-light photography. But with this new dedicated night mode, it leapfrogs the Pixel 2 and pulls in light and colors that your eye can't even see, all while keeping fine details clearly rendered. In night mode, the P20 Pro captures all the color and bright, vivid highlights that the Pixel 2 camera does, but with reduced noise and sharper fine details.
Source : https://www.androidcentral.com/huawei-p20-p20-pro-review