A Stable Diffusion 1.5 ControlNet that turns annotated game-terrain renders from Under Fire (a free, open-development WW2 RTS) into photorealistic aerial terrain. Trained on tstruk/under-fire-terrain-pairs: 600 pairs of reference renders and gpt-image-2 photorealistic targets, cut into aligned 512x512 patches and split by map.

Root weights: step 30,000 — a good balance between photographic quality and layout obedience; what the game itself runs.
checkpoint-018000/: step 18,000 — softer, more photographic textures than 30k with slightly weaker layout obedience; pairs well with a raised controlnet_conditioning_scale (1.2-1.5).
checkpoint-084000/: step 84,000 — the final checkpoint of the sweep. Most layout-faithful but visibly overtrained on this dataset size (harsher, oversharpened textures); published for comparison and study.

The base model (VAE, UNet, text encoder) stays frozen SD 1.5; only the ControlNet was trained (bf16 activations, fp32 weights, batch 16 effective, lr 1e-5 warmup+cosine, noise-prediction MSE).

Usage

python

import torch
from diffusers import (ControlNetModel, StableDiffusionControlNetPipeline,
                       UniPCMultistepScheduler)
from PIL import Image

controlnet = ControlNetModel.from_pretrained(
    "tstruk/under-fire-terrain-controlnet", torch_dtype=torch.bfloat16)
pipe = StableDiffusionControlNetPipeline.from_pretrained(
    "stable-diffusion-v1-5/stable-diffusion-v1-5",
    controlnet=controlnet, torch_dtype=torch.bfloat16, safety_checker=None)
pipe.scheduler = UniPCMultistepScheduler.from_config(pipe.scheduler.config)
pipe.to("cuda")

cond = Image.open("reference_512.png")   # a 512x512 reference-render patch
img = pipe(
    "ultra realistic aerial photograph of rural french countryside terrain, "
    "drone photo, neutral daylight",
    negative_prompt="blurry, low quality, oversharpened, noisy, grainy, "
    "jpeg artifacts, painting, cartoon, illustration, oversaturated, "
    "high contrast, hdr",
    image=cond, num_inference_steps=25, guidance_scale=4.0,
    controlnet_conditioning_scale=1.2,
).images[0]

About the prompts

Positive prompt: the model was trained with that exact fixed caption on every sample, so the caption is effectively part of the model. Keep it (or stay close to it) and the ControlNet's layout obedience holds. Appending style suffixes ("lush summer, golden hour") steers the look safely; replacing the caption wholesale weakens conditioning and shifts colours unpredictably.
Negative prompt: not used in training, but strongly recommended at inference — it visibly suppresses the oversharpened, oversaturated failure modes of the later checkpoints.
Guidance: 3.5-5.0. Lower is softer and more photographic; higher is punchier but amplifies overtraining artifacts.
controlnet_conditioning_scale: 1.0 default; raise to 1.2-1.5 to force stricter terrain-type placement on the prettier checkpoints.

The conditioning image must match the training distribution: the reference-render style documented on the dataset card (marker legend, ~21.6 px per world unit, camera tilt 35 degrees — the game's default tilt is 45 nowadays, so tilted conditioning should be captured at 35).

Full-scene usage

For whole game views rather than single patches: resize the frame so the ground scale matches training (~21.6 px per world unit, canonically 1718x915 per screen), crop into 512x512 tiles with ~110 px overlap, run the tiles as one batch, and stitch with linear blending across the overlaps. Two optional quality passes used in the game's own pipeline:

a second img2img pass over the stitched result at strength ~0.3 (same ControlNet conditioning) to add coherent micro-detail and melt seams,
Real-ESRGAN 2x on the final texture.

Notes and limitations

Trained at 512x512; for larger scenes, tile with overlap and blend seams.
The training targets drift geometrically from their references, so outputs follow layout semantically rather than pixel-exactly.
Water, villages and battle damage are rarer classes in the data; expect weaker fidelity there than on fields.
Intermediate sweep checkpoints (every 6k steps) are not published; 30k was the subjective quality peak, and beyond it textures grow progressively harsher from overfitting.

Credits

This model and its dataset exist thanks to Under Fire — a free, community-built WW2 real-time tactics game developed in the open, where this model bakes photorealistic terrain. Please credit underfire.io when building on this work.

License

Inherits CreativeML OpenRAIL-M from Stable Diffusion 1.5 (a ControlNet is initialized from, and contains weights derived from, the SD 1.5 UNet). The training dataset itself is CC0.