| name | nanobanana |
| description | AI image generation via Google Nano Banana (Gemini image models) with native aspect ratio and resolution control. Use when: (1) Generating images with specific aspect ratios (16:9, 9:16, 1:1, etc.), (2) Generating images at specific resolutions (1K, 2K, 4K), (3) Other skills need image generation backend (pptx-design, docx-design, xlsx-design), (4) User says 'generate image', 'nanobanana', 'nano banana', or needs AI image generation with precise dimension control. |
Nano Banana Image Generation
Generate images via Google's Nano Banana models with native aspect ratio and resolution control — no more prompt-only AR hacks.
Models
| Model | ID | Speed | Quality | Use When |
|---|
| Nano Banana 2 (default) | gemini-3.1-flash-image-preview | ~10s | Excellent, best instruction following, subject consistency | Default for all tasks |
| Nano Banana Pro | gemini-3-pro-image-preview | ~16s | Professional, 4K capable | User explicitly asks for pro/highest quality |
| Nano Banana Flash | gemini-2.5-flash-image | ~8s | Good, fast | Legacy, speed-only |
Default: Nano Banana 2. Use --model pro only if user explicitly requests pro quality. Nano Banana 2 is cheaper, faster, and has better subject consistency + instruction following than Pro.
Pricing
| Model | Resolution | Cost/Image | Batch (50% off) |
|---|
| Nano Banana Pro | 1K / 2K | $0.134 | $0.067 |
| Nano Banana Pro | 4K | $0.240 | $0.120 |
| Nano Banana Flash | All sizes | $0.039 | $0.0195 |
Cost examples:
- Typical PPTX deck (10 slides, Pro 2K backgrounds): ~$1.34
- Same deck with Flash: ~$0.39 (71% cheaper)
- Single 4K print-quality image (Pro): $0.24
Flash is ~3.4x cheaper than Pro. Use Flash for drafts, bulk generation, or when user is cost-conscious. Use Pro (default) for final/professional output.
Aspect Ratios
| AR | Name | Pixel Dims (2K) | Best For |
|---|
| 16:9 (default) | Widescreen | 2048 × 1152 | PPTX backgrounds, YouTube, desktop wallpaper |
| 9:16 | Portrait | 1152 × 2048 | Mobile, Instagram Stories, PPTX side panels |
| 1:1 | Square | 2048 × 2048 | Social media, icons, profile pics |
| 3:2 | Classic landscape | 2048 × 1365 | Photography, print |
| 2:3 | Classic portrait | 1365 × 2048 | Book covers, posters |
| 4:3 | Standard | 2048 × 1536 | Presentations (4:3 format), iPad |
| 3:4 | Standard portrait | 1536 × 2048 | Print, documents |
| 5:4 | Near-square landscape | 2048 × 1638 | Large prints |
| 4:5 | Instagram | 1638 × 2048 | Instagram feed posts |
| 21:9 | Ultrawide | 2048 × 878 | Cinematic, panoramic strips |
Default: 16:9. Show the table above when user asks for "list of aspect ratios" or "AR options".
Resolutions
| Size | Square (1:1) | Widescreen (16:9) | Portrait (9:16) | Gen Time | Best For |
|---|
| 1K | 1024 × 1024 | 1024 × 576 | 576 × 1024 | ~13s | Drafts, thumbnails, quick tests |
| 2K (default) | 2048 × 2048 | 2048 × 1152 | 1152 × 2048 | ~16s | PPTX/DOCX backgrounds, web, screen use |
| 4K | 4096 × 4096 | 4096 × 2304 | 2304 × 4096 | ~22s | Print, high-DPI displays, large format |
Default: 2K. Rationale: 2K at 16:9 (2048×1152) is the sweet spot for PPTX slide backgrounds (13.33"×7.5" at ~150 DPI). Sharp on screen, good for print, fast generation.
Show the table above when user asks for "list of resolutions" or "resolution options".
Usage
Script Location
All scripts are in the scripts/ subdirectory of this skill.
- Determine this SKILL.md file's directory path as
SKILL_DIR
- Script path =
${SKILL_DIR}/scripts/generate.py
Prerequisites
python3 -m pip install google-genai Pillow --quiet
Authentication
The script tries auth in this order:
GEMINI_API_KEY environment variable--api-key flag- OAuth credentials from Gemini CLI (
~/.gemini/oauth_creds.json)
If no auth found, the script prints setup instructions.
Commands
python3 ${SKILL_DIR}/scripts/generate.py --prompt "A moody cityscape at night" --output city.png
python3 ${SKILL_DIR}/scripts/generate.py --prompt "A cute cat" --output cat.png --ar 1:1 --size 4K
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Quick sketch" --output sketch.png --model flash
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Forest scene" --output forest.png --ar 9:16
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Same style but in winter" --output winter.png --reference summer.png
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Test concept" --output draft.png --size 1K
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Mountain range" --output pano.png --ar 21:9
Options
| Option | Description | Default |
|---|
--prompt, -p | Image generation prompt (required) | — |
--output, -o | Output file path | generated.png |
--ar | Aspect ratio | 16:9 |
--size | Resolution: 1K, 2K, 4K | 2K |
--model, -m | pro or flash | pro |
--reference, --ref | Reference image path(s) for vision input | — |
--api-key | Gemini API key (overrides env var) | — |
--json | Output result as JSON | false |
Output
On success, the script prints:
OK: saved to city.png (2048x1152, AR=1.78, model=gemini-3-pro-image-preview)
With --json:
{
"status": "ok",
"path": "city.png",
"width": 2048,
"height": 1152,
"ar": 1.78,
"model": "gemini-3-pro-image-preview",
"aspect_ratio": "16:9",
"image_size": "2K"
}
Recommended AR by Use Case
| Use Case | AR | Size | Why |
|---|
| Headshot / portrait photo | 3:4 | 2K | Classic portrait framing, natural phone-camera feel |
| Selfie (Instagram feed) | 4:5 | 2K | Instagram feed post standard |
| Selfie (Stories / full mobile) | 9:16 | 2K | Full vertical mobile screen |
| Profile pic / avatar | 1:1 | 2K | Square crop, universal across platforms |
| PPTX background | 16:9 | 2K | Matches widescreen slide ratio |
| PPTX side panel | 9:16 or 3:4 | 2K | Portrait crop for split layouts |
| Panoramic / cinematic | 21:9 | 2K | Ultrawide strip |
| Photography / print | 3:2 or 2:3 | 4K | Classic photo ratio, high-res for print |
| Book cover / poster | 2:3 | 2K | Tall portrait, standard print format |
When user asks for a "portrait", "selfie", or "headshot" without specifying AR, default to 3:4 at 2K.
Integration with Design Skills
When called from pptx-design, docx-design, or xlsx-design:
| Image Role | Recommended AR | Recommended Size |
|---|
| PPTX full-bleed background | 16:9 | 2K |
| PPTX side panel | 9:16 or 3:4 | 2K |
| PPTX content image | Match slot ratio | 2K |
| PPTX accent strip | 21:9 | 2K |
| DOCX cover banner | 16:9 or 3:1 (crop) | 2K |
| DOCX content illustration | 4:3 or 1:1 | 1K |
| XLSX cover image | 16:9 | 2K |
Key advantage over baoyu-danger-gemini-web: Native AR and resolution parameters mean the API returns images at the EXACT requested dimensions — no more prompt-only AR requests that Gemini ignores, no more post-generation cropping.
Post-Generation Verification
The script automatically verifies dimensions after generation. If the output doesn't match the requested AR (>5% deviation), it warns:
WARNING: AR mismatch — requested 16:9 (1.78), got 1024x1024 (1.00). Consider regenerating.
This should be rare with native AR params but serves as a safety net.
