Nano Banana PRO Image Generation

Generate professional AI images using Google's Nano Banana models via the Gemini API.

Prerequisites

• API key must be set as

  GEMINI_API_KEY

  environment variable
• Uses curl for all API calls (no SDK required)

Model Selection

gemini-3-pro-image-preview

gemini-2.5-flash-image

Default to PRO for quality work. Use Flash for rapid iterations or simple tasks.

CRITICAL: Prompt Engineering First

BEFORE calling the API, always craft an effective prompt. Read

references/prompting-guide.md

The Golden Rules

1. Describe scenes, don't list keywords - Write narrative descriptions, not tag soup
2. Use natural language - Full sentences with proper grammar
3. Be specific - Define subject, setting, lighting, mood, materials
4. Provide context - The "why" helps the model make better artistic decisions
5. Edit, don't re-roll - If 80% correct, ask for specific changes

The ICS Framework (Quick Reference)

For any image, specify:

• Image type: What kind of visual (photo, infographic, logo, sticker, etc.)
• Content: Specific elements, data, or information to include
• Style: Visual style, color palette, artistic approach

API Reference

Text-to-Image Generation

curl -s -X POST \
  "https://generativelanguage.googleapis.com/v1beta/models/gemini-3-pro-image-preview:generateContent" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [{
      "parts": [{"text": "YOUR_PROMPT_HERE"}]
    }],
    "generationConfig": {
      "responseModalities": ["TEXT", "IMAGE"],
      "imageConfig": {
        "aspectRatio": "16:9",
        "imageSize": "2K"
      }
    }
  }'

Image Editing (with input image)

curl -s -X POST \
  "https://generativelanguage.googleapis.com/v1beta/models/gemini-3-pro-image-preview:generateContent" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [{
      "parts": [
        {"text": "YOUR_EDIT_INSTRUCTION"},
        {"inline_data": {"mime_type": "image/png", "data": "BASE64_IMAGE_DATA"}}
      ]
    }],
    "generationConfig": {
      "responseModalities": ["TEXT", "IMAGE"]
    }
  }'

Configuration Options

aspectRatio

1:1

2:3

3:2

3:4

4:3

4:5

5:4

9:16

16:9

21:9

imageSize

1K

2K

4K

Google Search Grounding (Real-time Data)

Add

"tools": [{"google_search": {}}]

curl -s -X POST \
  "https://generativelanguage.googleapis.com/v1beta/models/gemini-3-pro-image-preview:generateContent" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [{"parts": [{"text": "Create an infographic of current tech stock prices"}]}],
    "tools": [{"google_search": {}}],
    "generationConfig": {
      "responseModalities": ["TEXT", "IMAGE"],
      "imageConfig": {"aspectRatio": "16:9"}
    }
  }'

Workflow

Step 1: Craft the Prompt

Use the ICS framework and prompting guide. Examples:

Photorealistic:

A photorealistic close-up portrait of an elderly Japanese ceramicist with deep wrinkles and a warm smile, inspecting a tea bowl. Soft golden hour light from a window. 85mm lens, shallow depth of field. Serene mood.

Infographic:

Create a clean, modern infographic explaining photosynthesis as a recipe. Show "ingredients" (sunlight, water, CO2) and "finished dish" (energy). Style like a colorful kids' cookbook page.

Product Shot:

High-resolution studio photograph of a matte black ceramic coffee mug on polished concrete. Three-point softbox lighting, 45-degree angle, sharp focus on rising steam. Square format.

Step 2: Generate Image

Use

scripts/generate-image.sh

./scripts/generate-image.sh "Your prompt here" output.png --ratio 16:9 --size 2K

Step 3: Process Response

The API returns base64-encoded image data. Extract and decode:

# Response contains: {"candidates":[{"content":{"parts":[{"inlineData":{"mimeType":"image/png","data":"BASE64..."}}]}}]}
# Extract with jq and decode:
cat response.json | jq -r '.candidates[0].content.parts[] | select(.inlineData) | .inlineData.data' | base64 -d > image.png

Common Use Cases

Landing Pages & Ads

• Use 16:9 or 21:9 for hero images
• Specify brand colors, modern/minimal style
• Include text requirements in prompt

Logos & Icons

• Use 1:1 aspect ratio
• Request "minimalist", "clean lines", "vector-style"
• Specify color scheme explicitly

Product Photography

• Describe lighting setup (softbox, natural, studio)
• Mention surface/background materials
• Include camera angle and lens type

Infographics

• Define data to visualize
• Specify style (corporate, playful, technical)
• Request clear text and labeled sections

Stickers & Illustrations

• Request "bold outlines", "kawaii", "cel-shading"
• Specify "white background" or "transparent background"
• Define color palette

Character Consistency (Multiple Images)

• PRO supports up to 14 reference images
• Explicitly state: "Keep facial features exactly the same as Image 1"
• Describe expression/pose changes while maintaining identity

Scripts

See

scripts/generate-image.sh

Detailed Prompting Guide

For advanced techniques including:

• Photorealistic scene templates
• Text rendering best practices
• Sequential art and storyboarding
• Dimensional translation (2D↔3D)
• Search grounding for real-time data

Read

references/prompting-guide.md