Upscale Image (Upscayl)

AI upscaling via upscayl-bin — the CLI shipped with the Upscayl GUI. Same Vulkan-accelerated realesrgan-ncnn-vulkan engine as standalone, but with Upscayl's curated model selection bundled.

When to use

• Low-res source needs to be enlarged for print or display.
• AI-generated image at 1024px wants 4096px output without re-prompting.
• Old photos / screenshots need detail recovery.

Do not use this skill when:

• The source is already large enough — upscaling rarely improves a 4K-native image.
• The user wants traditional bicubic / lanczos upscaling — fast-resize is the right tool (much faster, no AI).
• The image is text/document-heavy — upscalers can hallucinate glyph detail; consider tesseract re-OCR + re-typeset instead.

Inputs

1. Input — file or directory. Required.
2. Scale — 2, 3, or 4 (Upscayl's bundled models are 4× natively; 2× and 3× are produced by post-resize). Default 4.
3. Model — one of:
   • upscayl-standard-4x (default — best general-purpose photo upscaler).
   • upscayl-lite-4x (faster, lower quality, good for batches).
   • realesrgan-x4plus (classic, slightly different texture handling).
   • realesrgan-x4plus-anime (illustrations, line art, anime).
   • remacri-4x / ultramix-balanced-4x (alternative photo models if installed).
   • Or --model-path <dir> --model-name <name> to point at a custom model.
4. Output dir — default: <input-dir>/upscaled/. Skill never overwrites originals.
5. Output format — default png (lossless preserves the upscale fidelity). jpg option for size-sensitive batches (uses quality 92).
6. Recursive — --recursive for directory descent.
7. GPU — default auto-detect. --gpu <n> to pick a specific GPU. --cpu to force CPU (slow — only for headless boxes).

Procedure

1. Locate the binary. Check in order:

   • which upscayl-bin
   • /opt/Upscayl/resources/bin/upscayl-bin
   • ~/.var/app/org.upscayl.Upscayl/data/bin/upscayl-bin (Flatpak)
   • which realesrgan-ncnn-vulkan (fallback — same syntax, smaller model selection)

   If none found, point the user at install-deps (Upscayl install instructions: https://upscayl.org).

2. Locate the models directory. For upscayl-bin, typically:

   • /opt/Upscayl/resources/models/
   • ~/.var/app/org.upscayl.Upscayl/data/models/
   • User-custom dir at ~/.config/Upscayl/models/

   For standalone realesrgan-ncnn-vulkan, models are alongside the binary or in ./models/.

   Verify the requested model exists in the resolved dir (each model is a .param + .bin pair).

3. Enumerate inputs (image extensions only).

4. For each file:

   <binary> \
     -i "<input>" \
     -o "<output>.png" \
     -s 4 \
     -m "<models-dir>" \
     -n "<model>"

   The -s flag is fixed at the model's native scale (almost always 4). For non-4× output:

   • Scale 2 or 3: run 4× upscale, then post-resize down via vipsthumbnail to (orig × scale) dimensions:

     vipsthumbnail "<intermediate-4x.png>" --size "<target-w>x<target-h>" \
       --output "<final>.<ext>[Q=92]"

   • Scale 4 native: the upscaler output is final.

5. Output format conversion if --output-format jpg:

   cjpeg-mozjpeg -quality 92 -progressive < "<output>.png" > "<output>.jpg"
   rm "<output>.png"

6. Sequential, not parallel. Vulkan GPU is single-resource — running multiple upscales concurrently doesn't help and may OOM the GPU on large images. Run one at a time.
7. Memory awareness. For very large inputs (>4000px on the long side), the Vulkan tile size matters. Default is fine; if the binary reports OOM, retry with -t 100 (smaller tile = less VRAM, slightly slower). Surface this to the user rather than silently failing.

Output

• Upscaled images at <output-dir>/.
• Summary:
  • Files processed / failed.
  • Per-file: input dimensions → output dimensions, model used, elapsed seconds.
  • Total elapsed.
  • GPU device that was used (from upscayl-bin's stderr).

Notes

• Upscayl's upscayl-standard-4x produces visibly better results than vanilla realesrgan-x4plus on most photos — keep the default unless the user has a reason.
• Anime/illustration content: switch to realesrgan-x4plus-anime or one of the anime-specific Upscayl variants. Photo models smear line art.
• Compute time: ~5–20s per 1080p input on a mid-range GPU; 1–3 minutes per image on CPU. Batch a folder overnight for CPU runs.
• Output format default is PNG because JPEG re-encoding immediately after upscale undoes some of the perceptual gain. JPEG only when the user explicitly wants smaller files.
• Combining with other skills:
  • web-ready after upscale → use the gallery profile to ship the upscaled output to the web at sensible quality.
  • images-to-pdf after upscale → enlarge then print at higher DPI.
• This skill does not auto-install Upscayl or download models. The user owns that step. Models are typically several hundred MB total.