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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​

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​

ModelDescriptionMax ResolutionMax Input Images
gemini-2.5-flash-imageFast, efficient image generation (Nano Banana)1024px3
gemini-3-pro-image-previewAdvanced features, thinking mode, Google Search grounding (Nano Banana Pro)4K14

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

SizeDescription
1KDefault resolution
2KHigher resolution
4KMaximum 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<Image>> response = batchModel.submit(GeminiBatchRequest.from(
    prompts, "image-batch"));
String batchId = response.batchId();

// Poll for completion
while (!response.state().isTerminal()) {
    Thread.sleep(10000);
    response = batchModel.retrieve(batchId);
}

// Process results
if (response.state() == BatchState.SUCCEEDED) {
    for (Response<Image> imageResponse : response.responses()) {
        Image image = imageResponse.content();
        byte[] imageBytes = Base64.getDecoder().decode(image.base64Data());
        // Save or process each image
    }
}

// Clean up
batchModel.deleteBatchJob(batchId);

responses() and errors() are flat convenience views (never null, empty when there is nothing to report) that don't tell you which prompt produced which image. To map each outcome back to its prompt, use results(): it returns one BatchItemResult per request, in the same order as the submitted prompts, each being a BatchItemResult.Success (with response()) or a BatchItemResult.Failure (with error()):

List<BatchItemResult<Response<Image>>> results = response.results();
for (int i = 0; i < results.size(); i++) {
    BatchItemResult<Response<Image>> item = results.get(i);
    if (item.isSuccess()) {
        Image image = item.response().content();
        // Save or process the image generated for prompts.get(i)
    } else {
        BatchError error = item.error();
        System.err.println("Prompt #" + i + " failed: " + error.code() + " - " + error.message());
    }
}

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​