  Model pre-training is essential in human-centric perception. In this paper,
we first introduce masked image modeling (MIM) as a pre-training approach for
this task. Upon revisiting the MIM training strategy, we reveal that human
structure priors offer significant potential. Motivated by this insight, we
further incorporate an intuitive human structure prior - human parts - into
pre-training. Specifically, we employ this prior to guide the mask sampling
process. Image patches, corresponding to human part regions, have high priority
to be masked out. This encourages the model to concentrate more on body
structure information during pre-training, yielding substantial benefits across
a range of human-centric perception tasks. To further capture human
characteristics, we propose a structure-invariant alignment loss that enforces
different masked views, guided by the human part prior, to be closely aligned
for the same image. We term the entire method as HAP. HAP simply uses a plain
ViT as the encoder yet establishes new state-of-the-art performance on 11
human-centric benchmarks, and on-par result on one dataset. For example, HAP
achieves 78.1% mAP on MSMT17 for person re-identification, 86.54% mA on PA-100K
for pedestrian attribute recognition, 78.2% AP on MS COCO for 2D pose
estimation, and 56.0 PA-MPJPE on 3DPW for 3D pose and shape estimation.
