KeiSeiKit-1.0/skills/nano-banana/SKILL.md

name

description

nano-banana

Generates AI images using the nano-banana CLI (Gemini 3.1 Flash default, Pro available). Handles multi-resolution (512-4K), aspect ratios, reference images for style transfer, green screen workflow for transparent assets, cost tracking, and exact dimension control. Use when asked to "generate an image", "create a sprite", "make an asset", "generate artwork", or any image generation task for UI mockups, game assets, videos, or marketing materials.

nano-banana

AI image generation CLI. Default model: Gemini 3.1 Flash Image Preview (Nano Banana 2). Installed at: ~/tools/nano-banana-2/ Binary: ~/.bun/bin/nano-banana

Prerequisites

• Bun (installed at ~/.bun/bin/bun)
• FFmpeg + ImageMagick for transparent mode: brew install ffmpeg imagemagick
• Gemini API key at ~/.nano-banana/.env (get at https://aistudio.google.com/apikey)

Quick Reference

• Command: nano-banana "prompt" [options]
• Default: 1K resolution, Flash model, current directory

Core Options

Option	Default	Description
-o, --output	nano-gen-{timestamp}	Output filename (no extension)
-s, --size	1K	Image size: 512, 1K, 2K, or 4K
-a, --aspect	model default	Aspect ratio: 1:1, 16:9, 9:16, 4:3, 3:4, etc.
-m, --model	flash	Model: flash/nb2, pro/nb-pro, or any model ID
-d, --dir	current directory	Output directory
-r, --ref	-	Reference image (can use multiple times)
-t, --transparent	-	Green screen + FFmpeg background removal
--api-key	-	Gemini API key (overrides env/file)
--costs	-	Show cost summary

Models

Alias	Model	Use When
flash, nb2	Gemini 3.1 Flash	Default. Fast, cheap (~$0.067/1K image)
pro, nb-pro	Gemini 3 Pro	Highest quality (~$0.134/1K image)

Sizes & Costs

Size	Resolution	Flash Cost	Pro Cost
512	~512x512	~$0.045	Flash only
1K	~1024x1024	~$0.067	~$0.134
2K	~2048x2048	~$0.101	~$0.201
4K	~4096x4096	~$0.151	~$0.302

Aspect Ratios

Supported: 1:1, 16:9, 9:16, 4:3, 3:4, 3:2, 2:3, 4:5, 5:4, 21:9

Key Workflows

Basic Generation

nano-banana "minimal dashboard UI with dark theme"
nano-banana "cinematic landscape" -s 2K -a 16:9
nano-banana "quick concept sketch" -s 512

Pro Model (highest quality)

nano-banana "detailed portrait" --model pro -s 2K

Reference Images (Style Transfer / Editing)

nano-banana "change the background to pure white" -r dark-ui.png -o light-ui
nano-banana "combine these two styles" -r style1.png -r style2.png -o combined

Transparent Assets

nano-banana "robot mascot character" -t -o mascot
nano-banana "pixel art treasure chest" -t -o chest

The -t flag: green screen prompt -> FFmpeg colorkey + despill -> ImageMagick trim.

Exact Dimensions

# First -r: style reference, Last -r: blank image in target dimensions
nano-banana "pixel art character, 256x256" -r style.png -r blank-256x256.png -o sprite

Prompting Best Practices

1. Natural language — write sentences, not keyword lists
2. Be specific — include subject details, materials, lighting, mood
3. Include context — what is the image for (landing page, game asset, etc.)
4. Edit conversationally — refine existing generations with -r flag

Anti-Patterns (avoid)

• Tag-soup keywords: beautiful, HD, 4K, masterpiece
• Vague subjects: a nice landscape
• Missing mood/lighting: just describing objects without atmosphere
• Over-prompting: contradictory instructions

Good Prompt Examples

# UI mockups
nano-banana "clean SaaS dashboard with analytics charts, white background"
# Cinematic
nano-banana "cyberpunk cityscape at sunset, neon reflections on wet streets" -a 16:9 -s 2K
# Product
nano-banana "premium software product hero image, floating UI elements" --model pro
# Game assets
nano-banana "pixel art treasure chest, wooden with gold trim" -t -o chest
# Dark mode UI
nano-banana "Premium SaaS chat interface, dark mode, minimal, Linear-style aesthetic"

Use Cases

• Landing page assets (product mockups, hero images)
• Image editing (transform with text prompts + -r)
• Style transfer (combine multiple references)
• Marketing materials (feature illustrations)
• UI iterations (quick design variations)
• Transparent assets (icons, logos, mascots with -t)
• Game assets (sprites, characters, tilesets)
• Video production (visual elements for compositions)
• 3D website animations (generate keyframes for scroll-driven animations)

Cost Tracking

Every generation logged to ~/.nano-banana/costs.json.

nano-banana --costs

API Key Resolution Order

1. --api-key flag
2. GEMINI_API_KEY env var
3. .env in current directory
4. .env in repo root
5. ~/.nano-banana/.env