Imagen Skill Reference

Imagen Skill Reference

Setup

1. Get a Gemini API Key

1. Go to Google AI Studio
2. Click "Get API Key"
3. Create a new API key or use an existing one

2. Set Environment Variable

Windows (PowerShell):

$env:GEMINI_API_KEY = "your-api-key-here"

# To persist across sessions, add to your PowerShell profile:
Add-Content $PROFILE "`n`$env:GEMINI_API_KEY = 'your-api-key-here'"

Windows (CMD):

set GEMINI_API_KEY=your-api-key-here

# To persist, use System Properties > Environment Variables

macOS/Linux:

export GEMINI_API_KEY="your-api-key-here"

# Add to ~/.zshrc or ~/.bashrc to persist
echo 'export GEMINI_API_KEY="your-api-key-here"' >> ~/.zshrc

API Reference

Model

• Model ID: gemini-3-pro-image-preview (configurable via --model flag or GEMINI_MODEL env var)
• Endpoint: https://generativelanguage.googleapis.com/v1beta/models/{model}:streamGenerateContent

Image Sizes

Script Parameters

Python Script (Cross-Platform)

python scripts/generate_image.py <prompt> [output_path] [--size SIZE]

Environment Variables

Usage Examples

Basic Generation

python scripts/generate_image.py "A serene mountain landscape at dawn"

Custom Output Path

python scripts/generate_image.py "Minimalist logo design" "./assets/logo.png"

High Resolution

python scripts/generate_image.py --size 2K "Detailed portrait" "./high-res.png"

Small/Fast Generation

python scripts/generate_image.py --size 512 "Simple icon" "./icon.png"

Prompt Tips

For Best Results

1. Be specific: "A red sports car" vs "A cherry red 1967 Mustang convertible"
2. Include style: "in watercolor style", "photorealistic", "minimalist flat design"
3. Mention lighting: "golden hour lighting", "soft diffused light", "dramatic shadows"
4. Specify composition: "close-up", "wide angle", "from above", "centered"

Advanced Prompting Techniques

These techniques produce significantly better results for photorealistic and professional imagery:

Camera & Lens Specifications

Include specific photography parameters for authentic looks:

• Lens focal length: "85mm f/1.4 lens", "50mm prime", "35mm wide angle"
• Aperture: "shallow depth of field at f/1.8", "deep focus at f/8"
• Camera angle: "eye-level shot", "low angle looking up", "3/4 profile view"

Example: "Portrait shot with 85mm f/1.4 lens, shallow depth of field, subject sharp against soft bokeh background"

Lighting Architecture

Specify complete lighting setups for professional results:

• Three-point lighting: key light, fill light, rim/back light
• Catchlights: reflections in eyes for portraits
• Shadow quality: "soft shadows", "dramatic hard shadows", "subtle rim light"

Example: "Professional headshot with three-point lighting setup, soft key light from left, subtle fill light, rim light for hair separation, visible catchlights in eyes"

Film Stock & Era Aesthetics

Reference specific film stocks or eras for authentic period looks:

• Film stocks: "Kodak Portra 400 color palette", "Fujifilm Pro 400H tones", "Kodak Tri-X grain"
• Era aesthetics: "1990s disposable camera quality", "early-2000s digital camera look", "1970s Polaroid style"
• Grain and texture: "subtle film grain", "realistic sensor noise"

Example: "Casual portrait with Kodak Portra 400 color tones, natural film grain, 1990s aesthetic, soft warm highlights"

Facial Consistency (for portraits/people)

When generating or editing images with faces, explicitly state preservation requirements:

• "Keep the facial features exactly consistent"
• "Preserve original face structure and proportions"
• "Do not alter or change the face"

Material & Texture Details

Add realistic texture specifications:

• Skin: "natural skin texture with visible pores", "subtle skin imperfections"
• Fabric: "fine wool texture visible", "silk sheen and drape"
• Surfaces: "brushed metal finish", "weathered wood grain"

Example: "Close-up portrait showing natural skin texture with visible pores, fine fabric detail on collar, realistic hair strands"

Composition Framing

Be precise about framing and subject positioning:

• Shot types: "chest-up framing", "3/4 body shot", "full body"
• Positioning: "centered subject", "rule of thirds placement", "mirror selfie angle"
• Aspect ratio context: "portrait orientation", "landscape format", "square crop"

Example Prompts by Use Case

UI/Frontend:

• "A modern dashboard UI mockup with dark theme, showing analytics charts"
• "Clean minimalist app icon for a task management app, rounded square shape"
• "Hero image for a SaaS landing page, abstract gradient with geometric shapes"

Documentation:

• "Simple architecture diagram showing microservices connected by arrows"
• "Flowchart illustrating user authentication process"

Placeholders:

• "Professional headshot placeholder, silhouette style, neutral gray background"
• "Product image placeholder, simple box shape with 'Image Coming Soon' text"

Marketing/Creative:

• "Isometric illustration of a modern office workspace"
• "Gradient abstract background suitable for presentation slides"

Professional Portraits (using advanced techniques):

• "Corporate headshot, 85mm f/2.8 lens, three-point studio lighting, navy blue suit, neutral gray backdrop, subtle catchlights, chest-up framing, natural skin texture"
• "Casual lifestyle portrait, Kodak Portra 400 tones, natural window light, soft shadows, 3/4 body shot, authentic film grain, early-2000s digital aesthetic"

E-commerce & Product Photography:

• "Product photo of leather watch, 100mm macro lens, soft diffused lighting, visible leather texture and stitching, clean white background, subtle reflection"
• "Fashion flat-lay, overhead shot, soft natural lighting, fabric texture visible, minimalist composition"

Troubleshooting

"GEMINI_API_KEY not set"

Ensure the environment variable is set in your current shell:

Windows (PowerShell):

echo $env:GEMINI_API_KEY  # Should show your key

macOS/Linux:

echo $GEMINI_API_KEY  # Should show your key

"API request failed with HTTP status 400"

• Check your prompt for special characters that may break JSON
• Ensure the prompt isn't empty
• Verify API key is valid

"API request failed with HTTP status 429"

• Rate limited - wait a moment and retry
• Consider upgrading your API quota

"No image data found in response"

• The model may have refused the prompt (content policy)
• Try rephrasing the prompt
• Check if the model returned an error message in the response

Image is corrupted/won't open

• Ensure Python 3.6+ is installed
• Check if the full response was received (network issues)
• Verify output path is writable

Windows-specific issues

• Make sure Python is in your PATH
• Use forward slashes or escaped backslashes in paths

API Costs

Check Google AI pricing for current Gemini API costs. Image generation typically costs more than text generation.

Limitations

• Maximum prompt length varies by model
• Some content types may be restricted by Google's content policy
• Generated images are subject to Google's terms of service
• Rate limits apply based on your API tier