Un-/semi-/weakly-/self- Supervised Learning

Unsupervised Learning

[GWTA-CCNN] Almost Unsupervised Learning for Dense Crowd Counting (AAAI2019) [paper]

Semi-supervised Learning

[SSR] From Semi-Supervised to Transfer Counting of Crowds (ICCV2013) [paper]
[DG-GAN] Dense Crowd Counting Convolutional Neural Networks with Minimal Data using Semi-Supervised Dual-Goal Generative Adversarial Networks (CVPRW)[paper]

Weakly Supervised Learning

[MATT] Towards Using Count-level Weak Supervision for Crowd Counting (Pattern Recognition) [paper]
[GP] Gaussian Process Density Counting from Weak Supervision (ECCV) [paper]

Self-supervised Learning

[SL2R] Exploiting Unlabeled Data in CNNs by Self-supervised Learning to Rank (T-PAMI) [paper](extension of L2R)
[L2R] Leveraging Unlabeled Data for Crowd Counting by Learning to Rank (CVPR2018) [paper] [code]

Others (unclassed)

[CAC] Class-Agnostic Counting (ACCV2018) [paper] [code]