gemini-imagegen

Gemini Image Generation

Generate and edit images via Google Gemini's native multimodal image generation.

Model Selection

Model ID	Codename	Best for	Max resolution
gemini-2.5-flash-image	Nano Banana	Fast drafts, high-volume, low-latency	1K
gemini-3-pro-image-preview	Nano Banana Pro	Studio-quality, text rendering, complex prompts	4K

Default: gemini-3-pro-image-preview (Pro) unless speed/cost is a concern.

Setup

# Install (once)
# pip install google-genai

from google import genai
import os, base64

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

If GEMINI_API_KEY is missing, instruct the user to set it as an environment variable. Never ask the user to paste the key in chat.

Text-to-Image

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

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

response = client.models.generate_content(
    model="gemini-3-pro-image-preview",
    contents="A photorealistic cat on a rainbow sofa",
    config=types.GenerateContentConfig(
        response_modalities=["TEXT", "IMAGE"],
    ),
)

# Extract and save
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)
        break

Aspect Ratio

Set via image_config:

config=types.GenerateContentConfig(
    response_modalities=["TEXT", "IMAGE"],
    image_config=types.ImageConfig(
        aspect_ratio="16:9",  # for slides / widescreen
    ),
)

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

Common choices:

• Slides / presentations → 16:9
• Social media / portraits → 9:16 or 4:5
• Square thumbnails → 1:1

Image Editing (with reference image)

from google.genai import types
from pathlib import Path
import base64

ref_bytes = Path("input.jpg").read_bytes()

response = client.models.generate_content(
    model="gemini-3-pro-image-preview",
    contents=[
        types.Part(inline_data=types.Blob(mime_type="image/jpeg", data=base64.b64encode(ref_bytes).decode())),
        types.Part(text="Remove the background and replace with a sunset gradient"),
    ],
    config=types.GenerateContentConfig(
        response_modalities=["TEXT", "IMAGE"],
    ),
)