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

Model Identifier Best For

Nano Banana PRO gemini-3-pro-image-preview

Professional assets, text rendering, infographics, 4K output, complex multi-turn editing

Nano Banana gemini-2.5-flash-image

Fast generation, simple edits, lower cost

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 for comprehensive prompting strategies. Key principles:

The Golden Rules

• Describe scenes, don't list keywords - Write narrative descriptions, not tag soup

• Use natural language - Full sentences with proper grammar

• Be specific - Define subject, setting, lighting, mood, materials

• Provide context - The "why" helps the model make better artistic decisions

• 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

Parameter Values Notes

aspectRatio

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

Match use case

imageSize

1K , 2K , 4K

Use uppercase K; PRO model only for 4K

Google Search Grounding (Real-time Data)

Add "tools": [{"google_search": {}}] to generate images based on current information:

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 or call API directly:

./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 for a ready-to-use generation script.

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 .