Google AI Gemini Image Generation

Gemini can generate and edit images conversationally using specialized image models known as Nano Banana (Gemini 2.5 Flash Image) and Nano Banana Pro (Gemini 3 Pro Image Preview).

Table of Contents

• Overview
• Models Available
• GoogleAiGeminiImageModel
  • Basic Usage
  • Configuration
• Image Generation
  • Text-to-Image
  • Aspect Ratios
  • Image Sizes
• Image Editing
  • Adding and Removing Elements
  • Style Transfer
  • Inpainting
• Batch Image Generation
• Limitations
• Resources

Overview

Gemini's native image generation capabilities allow you to:

• Text-to-Image: Generate high-quality images from text descriptions
• Image Editing: Add, remove, or modify elements in existing images
• Style Transfer: Apply artistic styles to images
• Iterative Refinement: Conversationally refine images over multiple turns
• High-Fidelity Text Rendering: Generate images with legible, well-placed text

All generated images include a SynthID watermark.

Models Available

Model	Description	Max Resolution	Max Input Images
gemini-2.5-flash-image	Fast, efficient image generation (Nano Banana)	1024px	3
gemini-3-pro-image-preview	Advanced features, thinking mode, Google Search grounding (Nano Banana Pro)	4K	14

GoogleAiGeminiImageModel

Basic Usage

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-2.5-flash-image")
    .build();

Response<Image> response = imageModel.generate(
    "A nano banana dish in a fancy restaurant with a Gemini theme"
);

// Save the generated image
Image image = response.content();
byte[] imageBytes = Base64.getDecoder().decode(image.base64Data());
Files.write(Paths.get("nano-banana.png"), imageBytes);

Configuration

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-3-pro-image-preview")
    .aspectRatio("16:9")              // Output aspect ratio
    .imageSize("2K")                   // Resolution (Gemini 3 Pro only)
    .timeout(Duration.ofSeconds(120))
    .maxRetries(3)
    .logRequestsAndResponses(true)
    .safetySettings(...)               // Content safety settings
    .build();

Image Generation

Text-to-Image

Generate images from descriptive text prompts:

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-2.5-flash-image")
    .build();

// Photorealistic style
Response<Image> photo = imageModel.generate("""
    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, 85mm portrait lens, shallow depth of field.
    """);

// Stylized illustration
Response<Image> sticker = imageModel.generate("""
    A kawaii-style sticker of a happy red panda wearing a bamboo hat,
    munching on a leaf. Bold outlines, cel-shading, vibrant colors,
    white background.
    """);

// Logo design
Response<Image> logo = imageModel.generate("""
    A modern, minimalist logo for 'The Daily Grind' coffee shop.
    Clean, bold sans-serif font. Black and white. Circular design
    with a clever coffee bean element.
    """);

Aspect Ratios

Supported aspect ratios for both models:

Aspect Ratio	Use Case
1:1	Square, social media posts
2:3, 3:2	Portrait/landscape photos
3:4, 4:3	Standard photos
4:5, 5:4	Instagram posts
9:16, 16:9	Stories, YouTube thumbnails
21:9	Cinematic, ultrawide

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-2.5-flash-image")
    .aspectRatio("16:9")  // Widescreen format
    .build();

Image Sizes

Gemini 3 Pro Image Preview supports higher resolutions:

Size	Description
1K	Default resolution
2K	Higher resolution
4K	Maximum resolution

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-3-pro-image-preview")
    .aspectRatio("1:1")
    .imageSize("4K")  // High resolution output
    .build();

Image Editing

Adding and Removing Elements

Edit existing images by providing them alongside text prompts:

ImageModel imageModel = GoogleAiGeminiImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-2.5-flash-image")
    .build();

// Load the source image
Image sourceImage = Image.builder()
    .base64Data(Base64.getEncoder().encodeToString(
        Files.readAllBytes(Paths.get("cat.png"))))
    .mimeType("image/png")
    .build();

Response<Image> edited = imageModel.edit(
    sourceImage,
    "Add a small wizard hat on the cat's head. " +
    "Make it look natural with matching lighting."
);

Style Transfer

Transform images into different artistic styles:

Image cityPhoto = // ... load your image

Response<Image> stylized = imageModel.edit(
    cityPhoto,
    "Transform this city street into Vincent van Gogh's 'Starry Night' style. " +
    "Preserve the composition but render with swirling brushstrokes " +
    "and a dramatic palette of deep blues and bright yellows."
);

Inpainting

Modify specific elements while preserving the rest:

Image livingRoom = // ... load your image

Response<Image> edited = imageModel.edit(
    livingRoom,
    "Change only the blue sofa to a vintage brown leather chesterfield. " +
    "Keep everything else exactly the same."
);

Batch Image Generation

For generating multiple images at scale with 50% cost reduction:

GoogleAiGeminiBatchImageModel batchModel = GoogleAiGeminiBatchImageModel.builder()
    .apiKey(System.getenv("GOOGLE_AI_GEMINI_API_KEY"))
    .modelName("gemini-2.5-flash-image")
    .build();

List<String> prompts = List.of(
    "A nano banana dish in a Gemini-themed restaurant",
    "A kawaii sticker of a banana wearing a chef hat",
    "A photorealistic banana split dessert",
    "A minimalist logo for 'Nano Banana Co.'"
);

// Submit batch
BatchResponse<?> response = batchModel.createBatchInline(prompts, "image-batch");
BatchName batchName = getBatchName(response);

// Poll for completion
do {
    Thread.sleep(10000);
    response = batchModel.retrieveBatchResults(batchName);
} while (response instanceof BatchIncomplete);

// Process results
if (response instanceof BatchSuccess<?> success) {
    for (Image image : success.images()) {
        byte[] imageBytes = Base64.getDecoder().decode(image.base64Data());
        // Save or process each image
    }
}

// Clean up
batchModel.deleteBatchJob(batchName);

Limitations

• Languages: Best performance with EN, and supported languages including ar-EG, de-DE, es-MX, fr-FR, hi-IN, id-ID, it-IT, ja-JP, ko-KR, pt-BR, ru-RU, vi-VN, zh-CN
• Input: Audio and video inputs are not supported for image generation
• Output Count: The model may not always generate the exact number of images requested
• Input Images:
  • gemini-2.5-flash-image: Up to 3 input images
  • gemini-3-pro-image-preview: Up to 14 input images (including 5 human images for consistency)
• URL Images: URL-based images are not supported for editing; use base64-encoded images
• Watermark: All generated images include a SynthID watermark

Resources

• Gemini Image Generation Documentation
• Gemini API Models
• Batch API Documentation
• Image Generation Cookbook