---
language:
- en
license: mit
library_name: diffusers
tags:
- text-to-image
- stable-diffusion
- inference-time-alignment
- preference-optimization
- pg-map
- neurips-2026
pipeline_tag: text-to-image
---

# PG-MAP for Stable Diffusion 1.5

Custom diffusers pipeline for **PG-MAP** (Preference-Guided Adaptive MAP) on SD 1.5. Per-step joint optimization of conditioning $c$ and latent $z_t$ via a trajectory-level Gibbs-MAP / proximal energy objective, optionally guided by a frozen preference reward (PickScore by default).

NeurIPS 2026 — see [github.com/sophialanlan/PG-MAP](https://github.com/sophialanlan/PG-MAP) for the paper, full configs, and reproduction scripts.

## Install

```bash
pip install pg-map
# or
pip install git+https://github.com/sophialanlan/PG-MAP
```

## Usage

```python
from diffusers import DiffusionPipeline
from pgmap import sd15_defaults, FrozenRewardModel
import torch

pipe = DiffusionPipeline.from_pretrained(
    "runwayml/stable-diffusion-v1-5",
    custom_pipeline="sophialan/pg-map-sd15",
    torch_dtype=torch.float16,
    safety_checker=None,
).to("cuda")

cfg = sd15_defaults()                                       # paper defaults
reward = FrozenRewardModel("pickscore", device="cuda")

image = pipe(
    "a phoenix rising from ashes, vivid orange and red feathers",
    pg_map_config=cfg,
    reward_model=reward,
).images[0]
```

Passing `pg_map_config=None` falls through to the vanilla `StableDiffusionPipeline`, so the class is a strict superset of the parent.

## Method overview

Per denoising step $t$, PG-MAP solves the proximal MAP problem:

$$\mathcal{J}_t(c, z_t) = -\tfrac{1}{2\beta_{t|s}}\|r_t(c,z_t)\|^2 - \tfrac{1}{2\sigma_c^2}\|c-\mu_t\|^2 - \tfrac{1}{2\sigma_z(t)^2}\|z_t-z_t^{\text{ddim}}\|^2 + \lambda\,Q(\hat x_0(z_t,c), y)$$

with $K$ inner gradient-ascent steps and a schedule-adaptive trust region $\sigma_z(t)=\gamma\sqrt{1-\bar\alpha_t}$.

## Paper headline (SD 1.5, PartiPrompts $n=1632$, seed 123)

| Method | PickScore | HPS | Aesthetic | CLIP |
|---|---|---|---|---|
| PG-MAP (default)           | **56.8%** | 52.8% | 54.0% | 50.6% |
| Tuned-CFG + PG-MAP         | 53.6% | **66.0%** | **60.2%** | **56.0%** |

Win-rate vs. same-seed static baseline.

## Citation

```bibtex
@inproceedings{sun2026pgmap,
  title={{PG-MAP}: Joint {MAP} Optimization for Inference-Time Alignment of Diffusion and Flow-Matching Models},
  author={Sun, Ruolan and Polak, Pawel},
  booktitle={Advances in Neural Information Processing Systems (NeurIPS)},
  year={2026}
}
```

## License

MIT (see [LICENSE](https://github.com/sophialanlan/PG-MAP/blob/main/LICENSE)). Pretrained weights remain under their original licenses.