  Night-Time Scene Parsing (NTSP) is essential to many vision applications,
especially for autonomous driving. Most of the existing methods are proposed
for day-time scene parsing. They rely on modeling pixel intensity-based spatial
contextual cues under even illumination. Hence, these methods do not perform
well in night-time scenes as such spatial contextual cues are buried in the
over-/under-exposed regions in night-time scenes. In this paper, we first
conduct an image frequency-based statistical experiment to interpret the
day-time and night-time scene discrepancies. We find that image frequency
distributions differ significantly between day-time and night-time scenes, and
understanding such frequency distributions is critical to NTSP problem. Based
on this, we propose to exploit the image frequency distributions for night-time
scene parsing. First, we propose a Learnable Frequency Encoder (LFE) to model
the relationship between different frequency coefficients to measure all
frequency components dynamically. Second, we propose a Spatial Frequency Fusion
module (SFF) that fuses both spatial and frequency information to guide the
extraction of spatial context features. Extensive experiments show that our
method performs favorably against the state-of-the-art methods on the
NightCity, NightCity+ and BDD100K-night datasets. In addition, we demonstrate
that our method can be applied to existing day-time scene parsing methods and
boost their performance on night-time scenes.
