Gemini Image Generation
Generate and edit images using Google's Gemini API. Requires GEMINI_API_KEY environment variable.
Quick Reference
| Setting | Default | Options |
|---|---|---|
| Model | gemini-3-pro-image-preview | Use this for all generation |
| Resolution | 1K | 1K, 2K, 4K |
| Aspect Ratio | 1:1 | 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9 |
CLI Scripts
Generate Image
python scripts/generate_image.py "A cat in space" output.jpg
python scripts/generate_image.py "Epic landscape" landscape.jpg --aspect 16:9 --size 2K
python scripts/generate_image.py "Logo for Acme Corp" logo.jpg --aspect 1:1Edit Image
python scripts/edit_image.py input.jpg "Add a rainbow" output.jpg
python scripts/edit_image.py photo.jpg "Make it look like Van Gogh" artistic.jpgCore API Pattern
import os
from google import genai
from google.genai import types
client = genai.Client(api_key=os.environ["GEMINI_API_KEY"])
response = client.models.generate_content(
model="gemini-3-pro-image-preview",
contents=["Your prompt here"],
config=types.GenerateContentConfig(
response_modalities=['TEXT', 'IMAGE'],
),
)
for part in response.parts:
if part.text:
print(part.text)
elif part.inline_data:
image = part.as_image()
image.save("output.jpg") # Always use .jpg!Custom Resolution & Aspect Ratio
response = client.models.generate_content(
model="gemini-3-pro-image-preview",
contents=[prompt],
config=types.GenerateContentConfig(
response_modalities=['TEXT', 'IMAGE'],
image_config=types.ImageConfig(
aspect_ratio="16:9",
image_size="2K"
),
)
)Editing Images
from PIL import Image
img = Image.open("input.jpg")
response = client.models.generate_content(
model="gemini-3-pro-image-preview",
contents=["Add a sunset to this scene", img],
config=types.GenerateContentConfig(
response_modalities=['TEXT', 'IMAGE'],
),
)Multi-Turn Refinement
chat = client.chats.create(
model="gemini-3-pro-image-preview",
config=types.GenerateContentConfig(response_modalities=['TEXT', 'IMAGE'])
)
response = chat.send_message("Create a logo for 'Acme Corp'")
# Save first image...
response = chat.send_message("Make the text bolder and add a blue gradient")
# Save refined image...Prompting Best Practices
| Style | Prompt Pattern |
|---|---|
| Photorealistic | Include camera: lens, lighting, angle, mood |
| Stylized Art | Specify style explicitly: "kawaii-style", "cel-shading" |
| Text in Images | Be explicit: font style, placement, colors |
| Product Mockups | Describe lighting setup and surface |
Examples
# Photorealistic
"A photorealistic close-up portrait, 85mm lens, soft golden hour light, shallow depth of field"
# Stylized
"A kawaii-style sticker of a happy red panda, bold outlines, cel-shading, white background"
# Logo with text
"Create a logo with text 'Daily Grind' in clean sans-serif, black and white, coffee bean motif"
# Product mockup
"Studio-lit product photo on polished concrete, three-point softbox setup, 45-degree angle"Advanced Features
Google Search Grounding
response = client.models.generate_content(
model="gemini-3-pro-image-preview",
contents=["Visualize today's weather in Tokyo as an infographic"],
config=types.GenerateContentConfig(
response_modalities=['TEXT', 'IMAGE'],
tools=[{"google_search": {}}]
)
)Multiple Reference Images (Up to 14)
response = client.models.generate_content(
model="gemini-3-pro-image-preview",
contents=[
"Create a group photo of these people in an office",
Image.open("person1.jpg"),
Image.open("person2.jpg"),
Image.open("person3.jpg"),
],
config=types.GenerateContentConfig(
response_modalities=['TEXT', 'IMAGE'],
),
)Critical: File Format
Gemini returns JPEG by default. Always use .jpg extension.
# CORRECT
image.save("output.jpg")
# WRONG - causes "Image does not match media type" errors
image.save("output.png") # Creates JPEG with PNG extension!If PNG is Required
from PIL import Image
for part in response.parts:
if part.inline_data:
img = part.as_image()
img.save("output.png", format="PNG") # Explicit conversionMulti-Image Consistency
When generating a set of images that must look like the same scene (e.g., room makeovers, product variations, before/after sequences):
Lock the architecture, vary only the style.
- Write one detailed base description: dimensions, camera angle, window count/position, door location, furniture size, ceiling height, floor type
- Copy the base description identically into every prompt
- Change only the style portion: colors, materials, decor, lighting fixtures
Common failures without this technique:
- Windows appear/disappear between images
- Room dimensions change, furniture moves
- Result looks like N different rooms, not one room in N styles
Prompt structure:
[Camera/phone type]. [Detailed room architecture — identical across all images].
[Natural lighting description]. [Orientation].
**[STYLE VARIATION — only this part changes per image]**Tips:
- Include "iPhone photo" and "realistic lighting" for photorealistic output
- Add signs of life (mugs, remotes, books) so spaces feel inhabited, not staged
- "Before" images should look modern but tired, not derelict
- Always use portrait orientation (9:16 / 2:3) for social media slideshows
Notes
- All generated images include SynthID watermarks
- Default to 1K for speed; use 2K/4K when quality is critical
- For editing, describe changes conversationally—the model understands semantic masking
- Image-only mode won't work with Google Search grounding