  Open-set image recognition is a challenging topic in computer vision. Most of
the existing works in literature focus on learning more discriminative features
from the input images, however, they are usually insensitive to the high- or
low-frequency components in features, resulting in a decreasing performance on
fine-grained image recognition. To address this problem, we propose a
Complementary Frequency-varying Awareness Network that could better capture
both high-frequency and low-frequency information, called CFAN. The proposed
CFAN consists of three sequential modules: (i) a feature extraction module is
introduced for learning preliminary features from the input images; (ii) a
frequency-varying filtering module is designed to separate out both high- and
low-frequency components from the preliminary features in the frequency domain
via a frequency-adjustable filter; (iii) a complementary temporal aggregation
module is designed for aggregating the high- and low-frequency components via
two Long Short-Term Memory networks into discriminative features. Based on
CFAN, we further propose an open-set fine-grained image recognition method,
called CFAN-OSFGR, which learns image features via CFAN and classifies them via
a linear classifier. Experimental results on 3 fine-grained datasets and 2
coarse-grained datasets demonstrate that CFAN-OSFGR performs significantly
better than 9 state-of-the-art methods in most cases.
