Sebastiaan de With, writing on the Halide blog:
An iPhone XS will over- and underexpose the shot, get fast shots to freeze motion and retain sharpness across the frame and grab every best part of all these frames to create one image. That’s what you get out of the iPhone XS camera, and that’s what makes it so powerful at taking photos in situations where you usually lose details because of mixed light or strong contrast.
This isn’t the slight adjustment of Auto HDR on the iPhone X. This is a whole new look, a drastic departure from the “look” of every iPhone before it. In a sense, a whole new camera.
I don’t think this different look is a regression by any means — in fact, all of the photos I’ve seen from the iPhone XS indicate that this is a massive upgrade — but it is different. The rear cameras have large enough sensors and lenses that they are able to compensate for the higher noise created by faster shutter speeds through more intense noise reduction while preserving detail. When it comes to the front-facing camera’s much smaller sensor, though, it appears that the noise reduction is tuned to be a little more aggressive than expected, and it sounds like Apple is tweaking it.
One tip for RAW shooters:
To add insult to injury, iPhone XS sensor’s noise is just a bit stronger and more colorful than that of the iPhone X.
This isn’t the kind of noise we can easily remove in post-processing. This isn’t the gentle, film-like grain we previously saw in iPhone X and iPhone 8 RAW files.
As it stands today, if you shoot RAW with an iPhone XS, you need to go manual and under-expose. Otherwise you’ll end up with RAWs worse than Smart HDR JPEGs. All third-party camera apps are affected. Bizarrely, RAW files from the iPhone X are better than those from the iPhone XS.
With its bigger sensor, you should be able to get more detail out of an iPhone XS RAW image. But because this camera system is tuned to merge multiple exposures, it’s not quite as straightforward. This is a great piece for iPhone photographers.