Agent skill

nano-banana

Generate and edit images using Gemini's image generation API (Imagen 3). This skill should be used when creating images, illustrations, diagrams, editing existing images, or iteratively refining visual content through multi-turn conversations.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/Roasbeef/claude-files/tree/main/skills/nano-banana

SKILL.md

Nano Banana - Gemini Image Generation

This skill provides comprehensive access to Gemini's image generation capabilities, including text-to-image generation, image editing, multi-turn refinement, batch processing, and high-resolution output.

Prerequisites

  • API key set as GOOGLE_API_KEY or GEMINI_API_KEY environment variable
  • The scripts include a bundled virtual environment (.venv/) with google-genai pre-installed
  • Scripts can be called directly: ~/.claude/skills/nano-banana/scripts/generate_image.py

Available Models

Model ID Best For
Flash gemini-2.5-flash-image Fast generation, high volume, low latency
Pro gemini-3-pro-image-preview Professional quality, 4K, advanced reasoning

Capabilities Overview

Capability Script Description
Image Generation generate_image.py Create images from text prompts
Image Editing edit_image.py Modify existing images with instructions
Batch Generation batch_generate.py Generate multiple images in parallel
Multi-turn Editing chat_session.py Iterative refinement via conversation

Quick Start

Generate a Single Image

bash
python scripts/generate_image.py "a sunset over mountains" sunset.png

With options:

bash
python scripts/generate_image.py "modern office" office.png --model pro --aspect 16:9 --size 4K

Edit an Existing Image

bash
python scripts/edit_image.py photo.png "remove the background" result.png

Batch Generation

Create a prompts file (prompts.json):

json
[
    {"prompt": "slide 1: intro graphic", "filename": "slide_01.png", "aspect": "16:9"},
    {"prompt": "slide 2: data visualization", "filename": "slide_02.png", "aspect": "16:9"}
]

Generate all:

bash
python scripts/batch_generate.py prompts.json ./output/ --parallel 3

Or use a simple text file (one prompt per line):

bash
python scripts/batch_generate.py prompts.txt ./output/ --aspect 16:9

Multi-turn Editing Session

Start an interactive session:

bash
python scripts/chat_session.py --output-dir ./images/

Resume a previous session:

bash
python scripts/chat_session.py --session-file session.json

Send a single refinement:

bash
python scripts/chat_session.py --session-file session.json --message "make it more vibrant"

Script Reference

generate_image.py

Generate a single image from a text prompt.

Usage: python scripts/generate_image.py "prompt" output.png [options]

Options:
  --model, -m    Model: flash (default) or pro
  --aspect, -a   Aspect ratio: 1:1 (default), 16:9, 9:16, 21:9, 4:3, 3:4
  --size, -s     Resolution (pro only): 1K, 2K, 4K

edit_image.py

Edit an existing image using text instructions.

Usage: python scripts/edit_image.py input.png "instructions" output.png [options]

Options:
  --model, -m    Model: flash (default) or pro

batch_generate.py

Generate multiple images from a prompts file.

Usage: python scripts/batch_generate.py prompts.json output_dir/ [options]

Options:
  --model, -m     Model: flash (default) or pro
  --aspect, -a    Default aspect ratio: 1:1 (default)
  --parallel, -p  Number of parallel workers: 1 (default)
  --json          Output results as JSON

chat_session.py

Multi-turn image generation/editing session.

Usage: python scripts/chat_session.py [options]

Options:
  --model, -m        Model: flash (default) or pro
  --session-file, -s Path to session state file (JSON)
  --output-dir, -o   Directory for output images: . (default)
  --initial, -i      Initial prompt to start with
  --message          Send single message (non-interactive)

Best Practices

Prompting Tips

  1. Be specific: "A red sports car on a mountain road at sunset" works better than "a car".
  2. Describe style: Include art style, mood, lighting, and camera angle.
  3. Use negative space: Describe what should NOT be in the image when needed.

Editing Tips

  1. Target specific elements: "Change only the sky to purple" is better than "make it purple".
  2. Reference the original: "Keep the composition but change the color scheme".
  3. Iterative refinement: Use multi-turn sessions for complex edits.

Performance

  • Use flash model for quick iterations and high volume.
  • Use pro model for final production assets and 4K output.
  • Use batch generation with --parallel for multiple images.

Additional Resources

For detailed API documentation, see references/gemini-api.md. For prompting techniques, see references/prompt-guide.md. For common editing patterns, see references/editing-patterns.md.

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