  Face presentation attack detection (PAD) has become a thorny problem for
biometric systems and numerous countermeasures have been proposed to address
it. However, majority of them directly extract feature descriptors and
distinguish fake faces from the real ones in existing color spaces (e.g. RGB,
HSV and YCbCr). Unfortunately, it is unknown for us which color space is the
best or how to combine different spaces together. To make matters worse, the
real and fake faces are overlapped in existing color spaces. So, in this paper,
a learned distinguishable color-liked space is generated to deal with the
problem of face PAD. More specifically, we present an end-to-end deep learning
network that can map existing color spaces to a new learned color-liked space.
Inspired by the generator of generative adversarial network (GAN), the proposed
network consists of a space generator and a feature extractor. When training
the color-liked space, a new triplet combination mechanism of points-to-center
is explored to maximize interclass distance and minimize intraclass distance,
and also keep a safe margin between the real and presented fake faces.
Extensive experiments on two standard face PAD databases, i.e., Relay-Attack
and OULU-NPU, indicate that our proposed color-liked space analysis based
countermeasure significantly outperforms the state-of-the-art methods and show
excellent generalization capability.
