Interestingly, some phones now use a model of the camera sensor to detect how much noise there 'should' be (based on temperature, age of sensor, test results of

Interestingly, some phones now use a model of the camera sensor to detect how much noise there 'should' be (based on temperature, age of sensor, test results of the specific sensor from the factory, exposure time and light levels). They then only remove that much noise, hopefully leaving snow. Every other phone just has an algorithm to estimate how much noise is in an image by sampling a few patches - and that will remove snow.