NERVE / README.md
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---
license: apache-2.0
language:
- en
library_name: pytorch
pipeline_tag: image-to-image
tags:
- super-resolution
- image-restoration
- image-to-image
- sisr
- real-world-restoration
- pytorch
- onnx
- ncnn
- spandrel
- chainner
- edge
- mobile
datasets:
- Phips/lucid-cc0-v2-hc-512
---
# NERVE

**Norm-free Efficient Restoration for Various Edge devices**

A lightweight super-resolution architecture that is simple to train and fast to
run. Released models are **verified** with **traiNNer-redux** (training) and
**ONNX Runtime** + **ncnn** (inference). The op set is standard, so other
runtimes (**CoreML**, **TensorRT**, DirectML, ...) are expected to work too —
but they are not tested here.

Part of the **BODY** suite by **Philip Hofmann** — networks built to be
real-world usable first, not benchmark-chasing. See
[Relation to HEART](#relation-to-heart) for which one to pick.

All NERVE models were trained on a single consumer GPU (**RTX 3060, 12 GB**) — this network trains and runs on ordinary consumer hardware, no server-class GPU required.

**Links:** [NERVE](https://huggingface.co/Phips/NERVE) · [HEART](https://huggingface.co/Phips/HEART) · [NERVE demo](https://huggingface.co/spaces/Phips/nerve) · [HEART demo](https://huggingface.co/spaces/Phips/heart) · [convert a checkpoint](https://huggingface.co/spaces/Phips/nerve-convert) · [local app](https://github.com/Phhofm/nerve-app) · [train NERVE](https://github.com/Phhofm/nerve-train) · [train HEART](https://github.com/Phhofm/heart-train)

> Short version: copy `nerve_arch.py` into traiNNer-redux, train with the sample
> configs, then run the `.safetensors`, `.onnx`, or `.ncnn` models. One
> architecture, one size, no fused/unfused pairs. Details below.
![NERVE 4x on anime — input | bicubic | release | OTF GAN](examples/ani_compare.png)
*Input (as-is) | bicubic x4 | NERVE 4x release | NERVE 4x OTF GAN.*
![NERVE 4x on a noisy image](examples/noisy_compare.png)
![NERVE 4x on a Stable-Diffusion image](examples/stablediffusion_compare.png)
---
## Why NERVE?
There are strong and established SR networks already. This is the honest case
for when NERVE is worth your time — and when it is not.
This project comes out of a trainer's frustration rather than a benchmark goal.
After training hundreds of SISR models (see
[Phhofm/models](https://github.com/Phhofm/models)), the recurring annoyance was
networks that felt like *paper* networks: they chase leaderboard metrics with
techniques that leave you juggling an unfused and a fused checkpoint, or whose
dynamic-ONNX conversion is fragile. This network is the opposite of that — built
so a trainer can pick it up, train it, and convert it to dynamic ONNX without
headaches.
**Strengths of NERVE**
- **Real-world usability over metric chasing.** Trained on a CC0 dataset with
  the full Real-ESRGAN OTF degradation pipeline; the OTF GAN model restores
  degraded images, not just clean bicubic downsamples.
- **One file, one variant.** A single readable architecture file and one model
  size. No S/M/L matrix, no fused-vs-unfused checkpoints, nothing to fuse before
  deploy — what you train is what you ship.
- **Export just works.** Dynamic-shape ONNX (verified, ORT parity ~1e-5) and a
  clean ncnn conversion. Standard ops only (`Conv / Add / ReLU / DepthToSpace /
  Resize`).
- **Boring, stable training.** Norm-free, bf16 AMP, no gradient clipping, a
  single Charbonnier loss for the base stage.
- **Small and fast.** ~1.8M params — SPAN-class size but conv-only, suited to
  mobile, edge, web and game engines.
- **Maintainable for years.** One op set, no exotic dependencies, ~85-line arch.
**When to pick something else.** If the goal is maximum PSNR/LPIPS on academic
benchmarks, or a large transformer, NERVE is not aiming there — use HEART, HAT,
ATD, DAT2, or one of the community networks below. NERVE aims at simplicity,
deployability and hassle-free training.
**Credit where it is due.** None of this exists in a vacuum. SISR has many
strong architectures and generous community members, for example HAT, ATD and
DAT2, the community network work of [umzi](https://github.com/umzi2) and
[Kim2091](https://github.com/Kim2091), fdat by
[sharekhan](https://github.com/stinkybread), and
[the-database](https://github.com/the-database) (traiNNer-redux, its benchmarks
and its models). This list is far from complete — apologies to anyone not named;
the SISR community has a great many people contributing a great deal.
---
## Quickstart
### As a user (just want to upscale / restore images)
Pick a model and run it:
| I want to... | Use |
|---|---|
| upscale a clean image 4x | `models/4x_NERVE_release.safetensors` |
| upscale a clean image 2x | `models/2x_NERVE_release.safetensors` |
| restore a blurry / noisy / JPEG-y image 4x | `models/4x_NERVE_OTF_gan.safetensors` |
| run on-device / inside an engine | the `onnx/` or `ncnn/` files |

- **ONNX Runtime** (verified): use `onnx/*.onnx` (dynamic H/W). TensorRT /
  DirectML should work too (same op set) but are untested here.
- **ncnn** (verified, fp16): `ncnn/*.ncnn.param` + `*.ncnn.bin`. Feed images with
  `Mat.from_pixels`:
  ```python
  import ncnn
  net = ncnn.Net(); net.load_param("4x_NERVE_fp16.ncnn.param"); net.load_model("4x_NERVE_fp16.ncnn.bin")
  ex = net.create_extractor()
  ex.input("in0", ncnn.Mat.from_pixels(bgr_uint8, ncnn.Mat.PixelType.PIXEL_BGR2RGB, w, h))
  out = ex.extract("out0")[1]   # CHW float, 4x
  ```
  (Use `from_pixels`; the ncnn Python binding's raw-array constructor misbehaves
  on large inputs. Outputs are fp16, so expect small deviations at hard edges.)
- **chaiNNer**: load the `onnx/*.onnx` files directly. Loading the
  `.safetensors` via spandrel needs NERVE registered in your chaiNNer/spandrel
  build (not upstream yet).
- Input: RGB, any size. Output: 2x or 4x.

### As a trainer (want to train your own)

NERVE is a normal [traiNNer-redux](https://github.com/the-database/traiNNer-redux)
architecture — no special steps.

```bash
# 1. Add the architecture + its ICNR helper (auto-registers: traiNNer scans *_arch.py)
cp nerve_arch.py <traiNNer-redux>/traiNNer/archs/
cp icnr.py       <traiNNer-redux>/traiNNer/utils/   # ICNR init helper (not in upstream yet)
# 2. Copy a training config and point it at your data
cp configs/4x_NERVE_release.yml <traiNNer-redux>/options/
#    -> edit dataroot_gt / dataroot_lq in that file
# 3. Train
cd <traiNNer-redux>
python train.py -opt options/4x_NERVE_release.yml --auto_resume
# 4. Export to optimized dynamic ONNX (official converter)
cp configs/4x_NERVE_onnx.yml <traiNNer-redux>/options/
#    -> set path.pretrain_network_g to your trained checkpoint
python convert_to_onnx.py -opt options/4x_NERVE_onnx.yml
```

That is the whole workflow — 2 small files plus a config. The net is one file,
the config is one file, the checkpoint is one file — **no fusion step, no paired
fused/unfused weights.** (`icnr.py` is the only piece not in upstream
traiNNer-redux yet; it is the ICNR initializer for the PixelShuffle head.)

- `4x_NERVE_onnx.yml` exports dynamic-shape ONNX (opset 20) and can emit
  `fp32`, `fp16`, or `bf16` (`onnx.dtype`), with OnnxSlim optimization and a
  built-in PyTorch-vs-ONNX verify pass.
- Prefer no extra dependencies? `scripts/export_dynamic.py` is a tiny
  standalone exporter (torch + onnxruntime only).

**Start from a released pretrain** (skip the expensive early training) by
setting `path.pretrain_network_g` in your training config to a file from
`models/`:

| training stage | warm-start from |
|---|---|
| `4x_NERVE_release.yml` | `models/4x_NERVE_release.safetensors` (or the 2x one with `strict_load_g: false`) |
| `4x_NERVE_OTF_fidelity.yml` | `models/4x_NERVE_release.safetensors` |
| `4x_NERVE_OTF_gan.yml` | your OTF fidelity checkpoint |

**Training tips** (all NERVE models follow these):
- bf16 AMP is fine; no gradient clipping needed (norm-free net).
- `--auto_resume` is recommended for long runs.
- For real-world input, follow the chain: clean release -> OTF fidelity -> OTF GAN.

---

## Models

| File | Role | Notes |
|---|---|---|
| `models/2x_NERVE_release.safetensors` | **2x official pretrain** | clean bicubic, 31.84 dB / 0.9255 SSIM (Urban100) |
| `models/4x_NERVE_release.safetensors` | **4x official pretrain** | clean bicubic, 25.09 dB / 0.7531 SSIM (Urban100) |
| `models/4x_NERVE_OTF_fidelity.safetensors` | 4x OTF fidelity | restore degraded input; the pretrain for OTF GAN finetunes |
| `models/4x_NERVE_OTF_gan.safetensors` | 4x OTF GAN | **sharpest real-world output** (topiq 0.430 / lpips 0.290, Urban100 OTF val) |
| `models/2x_NERVE_OTF_gan.safetensors` | 2x OTF GAN | 2x restoration; **2x best** (PSNR 23.57 / SSIM 0.706 / TopIQ 0.576 / LPIPS 0.221, Urban100 OTF x2 val) |
| `onnx/4x_NERVE_1x3xHxW_fp32_op20.onnx` | 4x release, dynamic ONNX | onnxslim-optimized, fp32 |
| `onnx/2x_NERVE_1x3xHxW_fp32_op20.onnx` | 2x release, dynamic ONNX | onnxslim-optimized, fp32 |
| `onnx/4x_NERVE_OTF_fidelity_1x3xHxW_fp32_op20.onnx` | 4x OTF fidelity, dynamic ONNX | onnxslim-optimized, fp32 |
| `onnx/4x_NERVE_OTF_gan_1x3xHxW_fp32_op20.onnx` | 4x OTF GAN, dynamic ONNX | onnxslim-optimized, fp32 |
| `onnx/2x_NERVE_OTF_gan_1x3xHxW_fp32_op20.onnx` | 2x OTF GAN, dynamic ONNX | onnxslim-optimized, fp32 |
| `ncnn/4x_NERVE_fp16.ncnn.param` + `.bin` | 4x release, ncnn | fp16 weights |
| `ncnn/2x_NERVE_fp16.ncnn.param` + `.bin` | 2x release, ncnn | fp16 weights |
| `ncnn/4x_NERVE_OTF_fidelity_fp16.ncnn.param` + `.bin` | 4x OTF fidelity, ncnn | fp16 weights |
| `ncnn/4x_NERVE_OTF_gan_fp16.ncnn.param` + `.bin` | 4x OTF GAN, ncnn | fp16 weights |
| `ncnn/2x_NERVE_OTF_gan_fp16.ncnn.param` + `.bin` | 2x OTF GAN, ncnn | fp16 weights |

`models/*.safetensors` are plain EMA state dicts (no wrapper) — load them with
`nerve_arch.nerve(scale=N)`.

All released models (2x/4x release, 4x OTF fidelity, 4x OTF GAN) are final.

**Pretrain chain** (how the models relate):

```
2x_NERVE_release ──→ 4x_NERVE_release ──→ OTF fidelity ──→ OTF GAN
```

The release models are the shared starting point for anyone training NERVE:
warm-start from them (2x → 4x, or release → OTF fidelity → OTF GAN) to skip the
expensive early training.

---

## Examples

Real images are fed in **as-is** (not downscaled) and upscaled 4x. For each
image there are two comparisons:

- `examples/*_compare.png` — whole image at **full resolution**: **input** |
  **bicubic x4** | **NERVE 4x release** | **NERVE 4x OTF GAN**.
- `examples/*_1to1.png` — a **1:1 native-pixel center crop**.

The bicubic column is the baseline; the OTF GAN column is the released showcase
model. The source inputs are in `examples/inputs/`.

- `examples/realphoto_compare.png` (street scene)
- `examples/ani_compare.png` (anime)
- `examples/manga_compare.png` (manga)
- `examples/text_compare.png` (text)
- `examples/noisy_compare.png` (noisy input)
- `examples/stablediffusion_compare.png` (AI-generated)

## Architecture

```
5x5 conv stem → 24 × (Conv-ReLU-Conv + residual) → PixelShuffle → + bicubic(x)
```

- **~1.8M params**, pure convolution — **no attention, no normalization, no
  gating, no positional encoding, no reparameterization.**
- A **bicubic input residual** means the net only learns what bicubic upscaling
  misses — that's why it stays small and trains fast.
- **ICNR-initialized** PixelShuffle head (checkerboard-free by construction).
- The op graph is trivial: `Conv, Add, ReLU, DepthToSpace, Resize`. That's the
  entire reason it exports to dynamic ONNX and converts to ncnn (verified)
  without custom ops or fused/unfused pairs; CoreML is expected but untested.

## What we actually tested

Every design choice here came from a measured ablation, not a guess. The full
development log — including dead ends and raw numbers — is in
[`docs/ABLATIONS.md`](docs/ABLATIONS.md). Highlights:

- **Normalization**: removing LayerNorm beat the normed baseline by **+1.15 dB**
  at ~2x the training speed -> norm-free.
- **Depth/width sweep + capacity scaling**: quality improved with size; the
  sweep put the GAN quality knee at **1.80M** (0.69M -> 1.80M: lpips -0.015;
  1.80M -> 2.39M: only -0.002 more).
- **Dilation**: a dilated-conv A/B under the OTF recipe was **null** -> plain convs.
- **Checkerboard**: diagnosed a PixelShuffle phase-lock, fixed with ICNR plus
  *keeping aliased (nearest-exact) LR*. An anti-aliased-LR + sub-pixel-jitter
  variant made thin lines *worse* and was reverted.
- **OTF/GAN capability**: the small net trained productively under the full
  Real-ESRGAN OTF GAN recipe (no collapse).
- **Runtime validation**: every released `.safetensors` loads (strict) and runs;
  every `.onnx` loads in ONNX Runtime; the ncnn models were run at multiple input
  sizes up to 720x720 (2880x2880 output).
- **Deployability**: dynamic-ONNX export + ORT parity and ncnn conversion were
  verified at every stage (the numbers are in the log).
- **Not tested here** (community welcome): TensorRT / DirectML *speed* and
  fixed-shape static exports, CoreML, and on-device benchmarks. Train more
  variants, benchmark, and share — the arch is standard ops only.

## Training data & license

All released NERVE models were trained **only** on
[`Phips/lucid-cc0-v2-hc-512`](https://huggingface.co/datasets/Phips/lucid-cc0-v2-hc-512),
a **CC0** dataset — the released weights are clean to use commercially.

We did **not** optimize for benchmark leaderboards. If you want higher
PSNR/LPIPS numbers, training on larger academic datasets (DIV2K, Flickr2K,
LSDIR, ...) is expected to score better; NERVE is a normal architecture, train
it on whatever you like.

## Relation to HEART

NERVE and HEART are the two members of the **BODY** suite (by Philip Hofmann):
same philosophy (real-world usability > benchmark scores), different tiers.

| | **HEART** | **NERVE** |
|---|---|---|
| size | ~16.7M params | ~1.8M params |
| design | attention (FlashAttention-friendly) | pure convolution |
| use when | you want the **best quality** and have the compute (desktop, server, high-end device) | you want **speed, small size, and dead-simple deployment** (mobile, edge, web, game engines) |
| cost | heavier to run | a fraction of the cost |

Rule of thumb: **HEART for maximum quality, NERVE for maximum practicality.**
Both export to dynamic ONNX; NERVE additionally converts to ncnn cleanly
because it has no attention ops.

Side-by-side comparisons on the same inputs (`input | bicubic | both release
models | both OTF GAN models`), each with a 1:1 crop:
`examples/OST_009_nerve_vs_heart_*` and `examples/00003_nerve_vs_heart_*`
(Real-ESRGAN test set), plus `examples/realphoto_nerve_vs_heart_*` and
`examples/noisy_nerve_vs_heart_*`.

---

## Repository layout

```
nerve_arch.py                    the architecture (copy to traiNNer/archs/)
icnr.py                          ICNR init helper (copy to traiNNer/utils/; not in upstream yet)
configs/                         example training configs (+ 4x_NERVE_onnx.yml for ONNX export)
models/                          pretrained checkpoints (see table above)
onnx/                            dynamic fp32 ONNX (opset 20, onnxslim-optimized)
ncnn/                            ncnn fp16 param/bin
docs/ABLATIONS.md                the full development/ablation log (what we tested)
examples/                        real-image comparisons (input vs bicubic vs release vs GAN)
scripts/export_dynamic.py        checkpoint → dynamic ONNX exporter (+ ORT verify)
LICENSE                          Apache-2.0
```

## Help wanted (community welcome)

The goal here is **real-world usability** — easy training, hassle-free dynamic
ONNX, simple and robust to maintain — **not** leaderboard chasing. So NERVE's
strength is *simplicity for trainers*; there's still plenty worth measuring.
Pick anything below and open an issue/PR/discussion with your numbers.

**Benchmarks** (deliberately not chased here)
- Train on an academic dataset (DIV2K / Flickr2K / LSDIR) and compare against
  SPAN, SRVGGNetCompact, HAT, Real-ESRGAN (PSNR / SSIM / LPIPS).
- Perceptual metrics (LPIPS / TopIQ / MUSIQ) on real-world degraded images.

**Speed & deployment** (not benchmarked here)
- TensorRT / DirectML latency + peak VRAM on the dynamic ONNX.
- Static-shape ONNX (e.g. `1x3x256x256`) vs dynamic: speed + memory.
- fp16 vs fp32 ONNX.
- ncnn on-device (Android / iOS): latency + memory.
- CoreML conversion + on-device test.
- Mobile CPU (XNNPACK / ORT Mobile / ncnn).

**Models & code**
- More finetunes (illustration, manga, denoise, 1x restoration).
- Architecture experiments — see [`docs/ABLATIONS.md`](docs/ABLATIONS.md) for
  what we already tested (and rejected).

Small, measured contributions are welcome.

## License

Apache-2.0 (this repository's code and pretrained weights).

## Update — 2026-09-22: speed benchmark (honest numbers)

We ran a head-to-head **inference benchmark on an RTX 3060** using the
traiNNer-redux benchmark protocol (input `1x3x480x640`, fp16, 50 runs), against
the closest networks by parameter count:

| model | params | PyTorch fp16 | TensorRT fp16 | ncnn (Vulkan GPU) |
|---|---|---|---|---|
| **NERVE 2x** | 1.78M | 90.0 ms | 35.3 ms | 117 ms |
| SPAN_S 2x | 2.22M | 40.4 ms | **16.8 ms** | — |
| PLKSR_tiny 2x | 2.35M | 110.1 ms | 380.6 ms | — |
| compact 2x | 0.60M | 35.7 ms | 19.1 ms | — |

**NERVE does not win on speed.** SPAN_S is ~2.1x faster at a similar parameter
count, and compact is faster still. (PLKSR_tiny is slower in PyTorch and falls
apart in ONNX/TensorRT because its large-kernel/CCM ops don't map, so NERVE does
beat it there.)

That is neither a surprise nor a problem for what NERVE is for. **NERVE is not a
benchmark-chasing network.** It exists for ease of use and real-world usability:
one variant, one file, no fused/unfused checkpoint pairs, and a checkpoint that
converts to dynamic-shape ONNX, TensorRT and ncnn with no special handling.
Speed is good enough, not the goal.

Practical notes from the benchmark:
- **TensorRT is the fastest runtime for NERVE** (~2.5x over PyTorch), and it
  wants a **static shape** — that is where static exports actually matter.
- In ONNX Runtime, static vs dynamic made no measurable difference.
- fp16 ≈ bf16.
- **ncnn runs on the GPU via Vulkan** (117 ms vs 5.4 s on CPU), but that is the
  Python binding; native ncnn on a phone is the intended path, not a desktop race.

Choose SPAN if you want maximum speed. Choose NERVE if you want the simplest
thing to train, convert and ship.

## Update — 2026-09-25: 2x OTF GAN (and a patch/batch result)

Added a **2x OTF GAN** restoration model: warm-started from the 2x OTF fidelity
chain and finetuned with a **larger patch (`lq 128`) and batch (8)** for 150k
iterations, then validated against the previous 2x GAN (lq96/batch4, 150k) on
the same OTF-degraded Urban100 x2 set, full-frame:

| model (2x, same val) | PSNR | SSIM | TopIQ | LPIPS |
|---|---|---|---|---|
| 2x release (clean) | 20.36 | 0.525 | 0.407 | 0.486 |
| 2x OTF fidelity | **24.37** | **0.743** | 0.561 | 0.246 |
| 2x OTF GAN (lq96/b4) | 23.46 | 0.700 | 0.571 | 0.224 |
| **2x OTF GAN (lq128/b8)** | 23.57 | 0.706 | **0.576** | **0.221** |

The larger patch + batch improved **every** metric, so this is the released 2x
OTF GAN. (The tiled-vs-full-frame validation difference was measured and is
negligible: ~0.007 dB PSNR.)

## Update — 2026-09-29: fairness A/B vs SPAN_S (training stability)
We ran a controlled comparison against **SPAN_S**, a similar-sized network, to
check NERVE's claim of being simple and stable to train. Two experiments, each
with **identical configs for both networks** — only `network_g` differs, same
data, same degradation, same losses, same schedule, both **from scratch**.

**Read this fairly:** these are **short runs** (20k fidelity + 10k GAN on the
clean test; 30k on the OTF test), so they measure *early convergence and
stability*, not a fully-tuned best. SPAN_S was not tuned for itself, and NERVE
has fewer parameters (1.80M vs 2.24M). The configs are public so you can
reproduce or extend them.
### 1) Clean / bicubic — standard Urban100 x4
Training on standard bicubic HR/LR pairs; validation on the **standard
`urban100/lr_x4`** set (no self-made degradation). Fidelity 20k → GAN 10k.
| stage | NERVE (1.80M) | SPAN_S (2.24M) | difference |
|---|---|---|---|
| fidelity @20k (PSNR / SSIM) | **24.696 / 0.7368** | 23.991 / 0.7018 | **+0.70 dB / +0.035** |
| GAN @10k (PSNR / SSIM) | **24.694 / 0.7369** (peak 24.79) | 23.898 / 0.6930 (peak 24.08) | **+0.80 dB / +0.044** |

### 2) OTF — real-world degraded Urban100 x4

Training and validation with the Real-ESRGAN-style degradation pipeline, 30k.

| | NERVE (1.80M) | SPAN_S (2.24M) | difference |
|---|---|---|---|
| PSNR / SSIM @30k | **21.685 / 0.6266** | 21.413 / 0.6057 | **+0.27 dB / +0.021** |
| colour bias across training | flat (~2.6 / 1.6 / 1.7) | early spike to **4.96**, drifts back up | steadier |
### Verdict
* NERVE **converged faster and further** than SPAN_S in both settings, despite
  fewer parameters — and it was ahead at essentially every validation step.
* **Training stability:** in the OTF run SPAN_S's per-channel colour bias swung
  noticeably (a spike to ~4.96 early, then a slow climb) while NERVE stayed flat.
  In the clean run SPAN_S's **GAN stage lost PSNR** (24.08 → 23.90) whereas
  NERVE's held (24.79 → 24.69). That matches our own experience that SPAN can be
  finicky with GAN finetuning.
* **Caveat:** short runs and an untuned SPAN_S mean this is an indication, not a
  final verdict. It is, however, consistent across two independent setups.
### Evidence — clean / bicubic (standard Urban100 x4)
Validation PSNR (left) and SSIM (right):
![clean validation](docs/stability/clean/validation.png)
Training losses:
![clean losses](docs/stability/clean/losses.png)
Per-channel colour stability — flat lines near 0 mean no colour cast develops:
![clean colour stability](docs/stability/clean/colour_stability.png)
### Evidence — OTF (real-world degraded)
![otf validation](docs/stability/otf/validation.png)
![otf losses](docs/stability/otf/losses.png)
![otf colour stability](docs/stability/otf/colour_stability.png)
Raw numbers and the exact configs (reproduce it yourself):
[`docs/stability/clean/configs`](docs/stability/clean/configs) ·
[`docs/stability/otf/configs`](docs/stability/otf/configs) ·
[`colour_bias.csv` (clean)](docs/stability/clean/colour_bias.csv) ·
[`colour_bias.csv` (otf)](docs/stability/otf/colour_bias.csv)
## Update — 2026-09-30: TensorRT builder options (how to run NERVE fastest)
We swept TensorRT builder options for NERVE (via ONNX Runtime's TensorRT
provider) and applied the **same options to the other networks** for a fair
comparison. Input `1x3x480x640`, fp16, static shape, 50 runs, mean:
| model | TRT default | TRT `opt5 + CUDA graph` | gain |
|---|---|---|---|
| NERVE 2x (1.78M) | 33.24 ms | **31.80 ms** (31 FPS) | +4.5% |
| NERVE 4x (1.80M) | 38.43 ms | **33.82 ms** (30 FPS) | +13.6% |
| SPAN_S 2x (2.24M) | 16.62 ms | 14.91 ms (67 FPS) | +11.5% |
| compact 2x (0.60M) | 18.53 ms | 15.32 ms (65 FPS) | +20.9% |

![NERVE vs similar-sized networks — TensorRT fp16 speed](docs/nerve_speed.png)

**Verdict (honest).** The fastest TensorRT configuration we found is
**`trt_builder_optimization_level=5` plus CUDA graphs** — a free speedup for
every network here. NERVE gains 4.5–13.6%; it does **not** gain more than the
others, and it remains slower than SPAN_S and compact, as in the 2026-09-22
benchmark. TensorRT needs a **static shape**, so export one at the size you need.
### Exact command / config
Export a static fp16 ONNX at your target size, then create the session like this:
```python
import onnxruntime as ort
sess = ort.InferenceSession(
    "4x_NERVE_OTF_gan_1x3x480x640_fp16.onnx",
    providers=[
        ("TensorrtExecutionProvider", {
            "trt_fp16_enable": True,
            "trt_builder_optimization_level": 5,   # cheapest single win
            "trt_cuda_graph_enable": True,         # biggest win for small nets
            "trt_engine_cache_enable": True,       # cache the built engine
            "trt_engine_cache_path": "trt_cache",
            "trt_timing_cache_enable": True,
        }),
        "CUDAExecutionProvider",
    ],
)
```
Notes from the sweep:
* `trt_builder_optimization_level=5` alone was roughly neutral; the gain comes
  mostly from **CUDA graphs** (launch overhead matters for a net this small).
* `trt_tactic_sources` made no difference here (and CUDNN/CUBLAS names need a
  `+`/`-` prefix). Left at default.
* The first run builds the engine (can take ~1 min); the cache above makes
  subsequent starts instant.
* TensorRT was driven through ONNX Runtime; the same option names apply to the
  `trtexec` equivalents (`--builderOptimizationLevel=5`, `--useCudaGraph`).