Flux Image Generation API

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Prerequisites

1

Get API Key

Log in to laozhang.ai console to obtain your API key

2

Configure Billing Mode

Edit token settings and choose one of the following billing modes (same price for both):

• Volume Priority (Recommended): Uses balance billing first, automatically switches when balance is insufficient. Suitable for most users
• Pay-per-call: Direct deduction for each call. Suitable for strict budget control scenarios

Both modes have exactly the same price. Current Flux models include flux-2-pro, flux-2-max, flux-2-flex, flux-kontext-pro, and flux-kontext-max; check the console for real-time pricing.

If billing mode is not configured, API calls will fail. You must complete this configuration first!

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Flux Image Generation API

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🌟 Core Features

• 📐 Concrete Sizing: Flux 2 supports size and width / height
• 🎨 High-Quality Output: Supports common sizes such as 1024×1024, 1792×1024, and 1024×1792
• 🧩 Multi-Image Editing: Native Flux 2 uses input_image through input_image_8 for multiple reference images
• 💰 Pricing Details: Pricing is shown in the console for procurement review
• 🔧 JSON API: Text-to-image, single-image editing, and multi-image editing all use /v1/images/generations
• ⏱️ URL Validity: Generated result URLs valid for 10 minutes, download promptly
• 🔄 Reproducibility: Supports seed parameter for consistent results

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📋 Model Comparison

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📐 Size Parameters

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Flux 2 Common Sizes

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Legacy Flux Kontext Ratios

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🚀 Quick Start

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Flux 2 Text-to-Image cURL

curl -X POST "https://api2.laozhang.ai/v1/images/generations" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "flux-2-pro",
    "prompt": "A ruby red retro robot riding a yellow skateboard in front of a turquoise glass greenhouse, clean product illustration style",
    "n": 1,
    "size": "1792x1024"
  }'

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Flux 2 Python Example

import requests

API_KEY = "YOUR_API_KEY"

def generate_flux_image(prompt, size="1024x1024", model="flux-2-pro"):
    response = requests.post(
        "https://api2.laozhang.ai/v1/images/generations",
        headers={
            "Authorization": f"Bearer {API_KEY}",
            "Content-Type": "application/json",
        },
        json={
            "model": model,
            "prompt": prompt,
            "n": 1,
            "size": size,
        },
        timeout=240,
    )
    response.raise_for_status()
    return response.json()["data"][0]["url"]

image_url = generate_flux_image(
    "A cinematic product photo of a transparent smart speaker on a marble table",
    size="1024x1024",
)
print(image_url)

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📝 Parameter Details

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Flux 2 Text-to-Image Parameters

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💡 Best Practices

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1. URL Management and Download Strategy

import time
import requests

class FluxImageManager:
    """Flux image generation and download manager"""
    
    def __init__(self, api_key):
        self.api_key = api_key
        
    def generate_and_save(self, prompt, **kwargs):
        """Generate image and save immediately"""
        start_time = time.time()
        
        # Generate image
        image_url = generate_flux_image(prompt, **kwargs)
        if not image_url:
            return None
            
        # Download immediately (avoid timeout)
        elapsed = time.time() - start_time
        if elapsed > 540:  # Over 9 minutes
            print("⚠️ Warning: Approaching URL expiration time!")
        
        # Download and save
        filename = f"flux_{int(time.time())}.png"
        try:
            response = requests.get(image_url, timeout=30)
            response.raise_for_status()
            
            with open(filename, 'wb') as f:
                f.write(response.content)
                
            print(f"✅ Saved: {filename} (elapsed: {elapsed:.1f}s)")
            return filename
            
        except Exception as e:
            print(f"❌ Download failed: {e}")
            return None

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2. Model Selection Guide

• ✅ Recommended default model
• ✅ Text-to-image and multi-image editing
• ✅ Cost-sensitive projects
• ✅ Product images, posters, and general design assets

• ✅ More controllable editing workflows
• ✅ Complex design iteration
• ✅ Balanced quality and cost

• ✅ Highest quality requirements
• ✅ Final commercial assets
• ✅ Complex compositions and strong consistency needs

• ✅ Legacy integrations
• ✅ Daily design needs
• ✅ Batch content generation

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3. Prompt Optimization

# ❌ Too simple
prompt = "cat"

# ✅ Detailed description
prompt = """
A majestic orange tabby cat sitting by a window,
golden hour lighting, soft focus background,
professional pet photography style,
warm and cozy atmosphere
"""

# ✅ Use prompt_upsampling to enhance simple prompts
enhanced_result = generate_flux_image(
    prompt="cat by window",
    prompt_upsampling=True  # AI automatically expands and optimizes prompt
)

# ✅ Artistic style prompts
artistic_prompt = """
A surreal landscape painting in the style of Salvador Dali,
melting clocks draped over twisted trees,
vibrant sunset colors bleeding into a starry night sky,
hyper-detailed, dreamlike atmosphere
"""

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⚠️ Important Notes

1. URL Validity:
   • Generated image URLs are only valid for 10 minutes
   • Must download before expiration
   • Recommended to download immediately after generation
2. Parameter Passing:
   • Flux 2 text-to-image: pass size or width / height as top-level JSON fields
   • Flux 2 image editing: pass input_image and size parameters in JSON
   • Legacy Flux Kontext: use extra_body.aspect_ratio
3. Size Range:
   • Flux 2 common sizes: 1024x1024, 1792x1024, 1024x1792
   • For Flux 2 editing, use either size or width + height
   • Legacy Flux Kontext supports continuous aspect ratios from 3:7 to 7:3
4. Content Safety:
   • safety_tolerance parameter controls moderation strictness (0-6)
   • 0 = strictest, 6 = most lenient
   • Default value 2 suitable for most scenarios
5. Output Format:
   • Default JPEG format, smaller files
   • PNG format higher quality but larger files
   • Choose appropriate format based on use case
6. Prompt Processing:
   • prompt_upsampling auto-optimizes prompts
   • May change original intent, recommended to test first
   • Significant effect on simple prompts

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🔍 FAQ

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Q: Why do image URLs expire?

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Q: How is Flux different from other models?

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Q: How to choose between Pro, Flex, and Max?

• flux-2-pro: $0.0300/call, recommended default for most generation and editing
• flux-2-flex: $0.0600/call, suitable for more controlled and complex edits
• flux-2-max: $0.0700/call, suitable for highest-quality final commercial assets
• flux-kontext-pro/max: legacy Kontext-compatible models

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Q: Can I use any aspect ratio?

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Q: How to set safety_tolerance?

• 0-1: Corporate/commercial environment, strictest
• 2-3: General creation, balanced mode (recommended)
• 4-6: Artistic creation, more lenient

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Q: What does prompt_upsampling do?

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Q: How to ensure reproducible results?

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Q: How to avoid URL expiration in batch generation?

1. Download immediately after generation
2. Use concurrency control to avoid excessive processing time
3. Consider using async processing for efficiency

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🎯 Multi-Image Processing Solution

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Use Cases

• Pattern Transfer: Transfer design patterns onto clothing models
• Style Fusion: Combine characteristic elements from multiple images
• Product Composition: Fuse product, background, and design references into one scene

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Technical Approach

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Quick Start

curl -X POST "https://api2.laozhang.ai/v1/images/generations" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "flux-2-pro",
    "prompt": "Use image 1 as the red robot, image 2 as the greenhouse background, and image 3 as the skateboard. Create one fused scene.",
    "input_image": "https://example.com/source_1_red_robot.png",
    "input_image_2": "https://example.com/source_2_glass_greenhouse.png",
    "input_image_3": "https://example.com/source_3_yellow_skateboard.png",
    "width": 1792,
    "height": 1024,
    "output_format": "png"
  }'

cd ~/Downloads
export LAOZHANG_API_KEY="YOUR_API_KEY"

IMG1=$(base64 < source_1_red_robot.png | tr -d '\n')
IMG2=$(base64 < source_2_glass_greenhouse.png | tr -d '\n')
IMG3=$(base64 < source_3_yellow_skateboard.png | tr -d '\n')

curl -X POST "https://api2.laozhang.ai/v1/images/generations" \
  -H "Authorization: Bearer $LAOZHANG_API_KEY" \
  -H "Content-Type: application/json" \
  --data-binary @- \
  -o flux_local_multi_response.json <<EOF
{
  "model": "flux-2-pro",
  "prompt": "Combine the three provided reference images into one coherent new image. Use image 1 as the red robot, image 2 as the turquoise glass greenhouse background, and image 3 as the yellow skateboard. The final image must clearly include details from all three references, not a collage or split-screen.",
  "input_image": "data:image/png;base64,$IMG1",
  "input_image_2": "data:image/png;base64,$IMG2",
  "input_image_3": "data:image/png;base64,$IMG3",
  "width": 1792,
  "height": 1024,
  "output_format": "png"
}
EOF

import requests

API_KEY = "YOUR_API_KEY"

response = requests.post(
    "https://api2.laozhang.ai/v1/images/generations",
    headers={
        "Authorization": f"Bearer {API_KEY}",
        "Content-Type": "application/json",
    },
    json={
        "model": "flux-2-pro",
        "prompt": "Use image 1 as the subject, image 2 as the background, and image 3 as a design element. Fuse them into one coherent scene.",
        "input_image": "https://example.com/image1.png",
        "input_image_2": "https://example.com/image2.png",
        "input_image_3": "https://example.com/image3.png",
        "width": 1792,
        "height": 1024,
        "output_format": "png",
    },
    timeout=240,
)
print(response.json())

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🔗 Related Resources

• Complete Example Code
• Flux Image Edit API - Edit existing images
• Pricing Calculator - Real-time price query
• Online Demo - Test Flux effects