Nano Banana

Nano Banana 2 Image Generation

Generates professional images with Nano Banana 2 (gemini-3.1-flash-image-preview). Pro-level quality at Flash speed -- 512px to 4K, various aspect ratios, multilingual text rendering support.

When to Use This Skill

ALWAYS use this skill when the user:

• Asks for any image, graphic, illustration, or visual
• Wants a thumbnail, featured image, or banner
• Requests icons, diagrams, or patterns
• Asks to edit, modify, or restore a photo
• Uses words like: generate, create, make, draw, design, visualize

Do NOT attempt to generate images through any other method.

Prerequisites

1. Install Python SDK

pip install google-genai

2. Set API Key (paid required -- free keys cannot generate images)

export GEMINI_API_KEY="your-paid-api-key"

Or auto-load from project .env file.

Image Generation (Python SDK -- Default Method)

Basic Generation

import os
from google import genai
from google.genai import types

client = genai.Client(api_key=os.environ["GEMINI_API_KEY"])

response = client.models.generate_content(
    model="gemini-3.1-flash-image-preview",
    contents="Your prompt here",
    config=types.GenerateContentConfig(
        response_modalities=["IMAGE", "TEXT"],
    )
)

for part in response.candidates[0].content.parts:
    if part.inline_data is not None:
        with open("output.png", "wb") as f:
            f.write(part.inline_data.data)

Advanced Options

Resolution Control

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    image_size="4K",  # "512", "1K", "2K" (default), "4K"
)

Aspect Ratio

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    aspect_ratio="16:9",  # "1:1", "16:9", "9:16", "4:3", "3:4", "4:1", "1:4", "8:1", "1:8"
)

Thinking Level (for complex prompts)

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    thinking_level="high",  # "minimal" (default), "high", "dynamic"
)

Execution Pattern

Always follow this pattern when generating images:

Step 1: Determine Output Path

• If the project has an assets/ directory, save there
• Otherwise save to current directory
• Name files appropriately (e.g., hero.png, thumbnail.png, logo.png)
• If using a dedicated nanobanana-output/ output directory, adding it to .gitignore is recommended

Step 2: Load API Key

# Try environment variable -> .env file in order
import os
api_key = os.environ.get("GEMINI_API_KEY")
if not api_key:
    # Attempt to load from .env file
    for env_path in [".env", "../.env", os.path.expanduser("~/.env")]:
        if os.path.exists(env_path):
            with open(env_path) as f:
                for line in f:
                    if line.startswith("GEMINI_API_KEY="):
                        api_key = line.strip().split("=", 1)[1]
                        break
        if api_key:
            break

Step 3: Optimize Prompt

Good prompt structure:

1. Subject: What to generate
2. Details: Appearance, colors, textures
3. Setting: Location, background, environment
4. Style: Realistic, illustration, 3D render, etc.
5. Lighting: Natural, dramatic, soft
6. Composition: Close-up, wide shot

Step 4: Execute Generation + Verify Result

After generation, always verify the image using the Read tool and show it to the user.

Common Sizes

Model Selection

Always default to NB2 -- Pro only when highest quality is needed.

Multi-Turn Editing

When modification is requested after image generation, edit conversationally:

# First generation
chat = client.chats.create(model="gemini-3.1-flash-image-preview")
response1 = chat.send_message(
    "A red apple on a wooden table",
    config=types.GenerateContentConfig(response_modalities=["IMAGE", "TEXT"])
)

# Edit (preserving previous context)
response2 = chat.send_message(
    "Add a green leaf on top of the apple",
    config=types.GenerateContentConfig(response_modalities=["IMAGE", "TEXT"])
)

Prompt Tips

1. Be specific: Include style, mood, color, composition details
2. When no text needed: Add "no text"
3. Style reference: "editorial photography", "flat illustration", "3D render", "watercolor"
4. Aspect ratio context: "wide banner", "square thumbnail", "vertical story"
5. Complex scenes: Use thinking_level="high"

Troubleshooting

Gemini CLI Method (Alternative)

If Python SDK is unavailable, generate via Gemini CLI:

gemini -y -m gemini-3.1-flash-image-preview -p "Generate image and save as output.png: your prompt here"

Note: Gemini CLI requires Google account authentication, and the image generation model may require additional verification.