nanobanana

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.

1. Determine this SKILL.md file's directory path as SKILL_DIR
2. Script path = ${SKILL_DIR}/scripts/generate.py

Prerequisites

python3 -m pip install google-genai Pillow --quiet

Authentication

The script tries auth in this order:

1. GEMINI_API_KEY environment variable
2. --api-key flag
3. OAuth credentials from Gemini CLI (~/.gemini/oauth_creds.json)

If no auth found, the script prints setup instructions.

Commands

# Basic image generation (defaults: pro model, 16:9, 2K)
python3 ${SKILL_DIR}/scripts/generate.py --prompt "A moody cityscape at night" --output city.png

# Specify aspect ratio and resolution
python3 ${SKILL_DIR}/scripts/generate.py --prompt "A cute cat" --output cat.png --ar 1:1 --size 4K

# Use non-pro (flash) model
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Quick sketch" --output sketch.png --model flash

# Portrait for mobile / side panels
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Forest scene" --output forest.png --ar 9:16

# With reference image (style transfer / variation)
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Same style but in winter" --output winter.png --reference summer.png

# Low-res draft
python3 ${SKILL_DIR}/scripts/generate.py --prompt "Test concept" --output draft.png --size 1K

# Ultrawide panoramic strip
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.