Sr Diffusion

It is a deterministic 3.02M-parameter image-space detail branch on top of the frozen dual-context LSDIR Stage 2 step 98000 condition encoder and frozen Stage 1 decoder. The run completed 100086 micro-steps, exactly three epochs, and selected step 99500 by eval/detail_score.

Selected ordinary photo_detail_mix val100 result:

aggregate PSNR delta vs frozen base: +0.1646 dB
mean PSNR delta vs frozen base: +0.1888 dB
SSIM delta vs frozen base: +0.00647
PSNR wins: 99/100
detail wins: 100/100

Exploratory strict-bicubic DIV2K five-center-crop result:

mean RGB PSNR: 31.9513 dB
vs frozen base: +0.2102 dB
vs detail v1c: +0.1358 dB
wins: 5/5

The strict-bicubic result is not a formal SOTA benchmark. It uses five 512x512 center crops, PIL bicubic x4 degradation, full-image RGB PSNR, and no border shave.

Formal full-image clean-bicubic benchmark, reported as Y PSNR / Y SSIM:

This uses public x4 LR pairs, MATLAB-compatible BT.601 Y, a four-pixel border shave, and MATLAB-style SSIM. V1d improves its frozen base on all four datasets. These clean-bicubic fidelity results are not a claim of classical-SR SOTA or a substitute for real-degradation and perceptual evaluation.

For scale, the official SwinIR classical x4 checkpoint reaches 31.0838 / 0.85228 on the same DIV2K evaluator, +0.9235 dB Y PSNR ahead of detail v1d. The next clean-fidelity priority is therefore the Stage 2/base reconstruction path rather than a larger detail branch.

A clean-bicubic Stage 2 continuation improved its task-specific val100 proxy only gradually and plateaued around 25.05. Learning-rate probes did not change that conclusion: 20x LR collapsed, while a 5x from-init run matched the original LR within evaluation noise. These val100 values are not directly comparable with the formal full-image Y-channel benchmark above.

The signed-high-frequency residual diffusion path was evaluated and rejected: longer noise-MSE training collapsed residual magnitude and seed diversity toward zero. The next separate generative research path keeps the deterministic base and validated learned mask frozen, then tests a small bounded mask-weighted patch perceptual/adversarial head with fidelity and artifact guardrails.

Latest Masked Detail Research Candidate

The learned-mask-gated v2 candidate is:

checkpoints/detail_branch_v2_masked_photo130k_lsdir_best38000.pt

It combines the frozen 460K-parameter detail-mask predictor step 3250 with the 3.02M-parameter detail branch and a soft-mask floor of 0.05. On ordinary photo_detail_mix val100, selected step 38000 improves the frozen base by +0.18177 dB aggregate PSNR, +0.20432 dB mean PSNR, and +0.00755 SSIM, with 100/100 wins.

The score plateaued after step 38000 and fixed grids were nearly indistinguishable from nearby checkpoints. It modestly improves metrics over v1d but does not visibly recover the missing fine texture that motivated the experiment. It is therefore a reproducible research option, not the public default.

On the same formal 219-image clean-bicubic benchmark, masked v2 reaches 30.1636 / 0.83512, 31.9495 / 0.89534, 28.4257 / 0.78102, and 25.8922 / 0.78022 on DIV2K, Set5, Set14, and Urban100. It improves v1d on all four datasets, but the overall gain is only +0.0114 dB Y PSNR and +0.00118 Y SSIM.

Download

From a LuSIR GitHub clone:

python scripts/download_hf_checkpoints.py --preset detail_branch_v1d

Other useful presets include:

stage2_guarded_detail_v2
residual_refiner_v2
stage2_photo130k_lsdir_dual
detail_branch_v1b
detail_branch_v2_masked
photo100k_xl_stage4_edge

The public Colab default is now the T4-friendly guarded-detail Stage 2 v2 checkpoint with tile batch size 1. Residual refiner v2 remains available as the conservative deterministic option. Detail v1d and masked detail v2 remain research options in the Colab WebUI with single-image and tiled inference.

Runtime Paths

public deterministic default:
LR -> guarded-detail Stage 2 v2 step 10000 -> Stage 1 decoder -> SR

conservative deterministic option:
LR -> Stage 2 XL -> residual refiner v2 -> Stage 1 decoder -> SR

selected detail research path:
LR -> dual-context LSDIR Stage 2 -> Stage 1 decoder
-> learned detail mask -> masked detail branch v2 -> SR

generative comparison:
LR -> Stage 2 condition encoder -> Stage 3 OR Stage 4 diffusion U-Net
-> Stage 1 decoder -> SR

Stage numbers describe training order. Stage 3 and Stage 4 are alternative diffusion checkpoints, not modules executed sequentially.

License

• Checkpoints, generated samples, metrics, and other non-code artifacts: CC BY-NC 4.0.
• Source code: PolyForm Noncommercial License 1.0.0.

Commercial use is not permitted without separate written permission.