  Neural radiance fields (NeRF) have shown great success in novel view
synthesis. However, recovering high-quality details from real-world scenes is
still challenging for the existing NeRF-based approaches, due to the potential
imperfect calibration information and scene representation inaccuracy. Even
with high-quality training frames, the synthetic novel views produced by NeRF
models still suffer from notable rendering artifacts, such as noise and blur.
To address this, we propose NeRFLiX, a general NeRF-agnostic restorer paradigm
that learns a degradation-driven inter-viewpoint mixer. Specially, we design a
NeRF-style degradation modeling approach and construct large-scale training
data, enabling the possibility of effectively removing NeRF-native rendering
artifacts for deep neural networks. Moreover, beyond the degradation removal,
we propose an inter-viewpoint aggregation framework that fuses highly related
high-quality training images, pushing the performance of cutting-edge NeRF
models to entirely new levels and producing highly photo-realistic synthetic
views. Based on this paradigm, we further present NeRFLiX++ with a stronger
two-stage NeRF degradation simulator and a faster inter-viewpoint mixer,
achieving superior performance with significantly improved computational
efficiency. Notably, NeRFLiX++ is capable of restoring photo-realistic
ultra-high-resolution outputs from noisy low-resolution NeRF-rendered views.
Extensive experiments demonstrate the excellent restoration ability of
NeRFLiX++ on various novel view synthesis benchmarks.
