The most significant improvement of Xiaomi 17 Ultra is the inclusion of LOFIC technology.

To briefly explain, if a pixel is trap for capturing light, then the full-well capacity is the number of photons a pixel can store. Theoretically, the larger the full-well capacity, the higher the dynamic range. However, it's important to note that simply increasing the full-well capacity primarily ensures that highlights don't overflow. In low-light conditions, it's difficult to fill the entire image, and to improve the image quality, the gain must be artificially increased, leading to more noise in shadows. LOFIC solves this problem by equipping each pixel with two capacitors, one large and one small, and opening a channel between them. Photons first enter the small capacitor, filling it before overflowing into the large capacitor. The benefits of this are obvious: it simultaneously ensures detail in highlights and clarity in shadows.

Source: WekiHome

@Xiaomi