FLUX.1 [pro] Fill | [image-to-image]
Black Forest Labs' FLUX.1 [pro] delivers professional-grade inpainting at $0.05 per megapixel. Trading broad creative generation for surgical precision, this endpoint excels at targeted modifications, replacing objects, filling gaps, or seamlessly blending new elements into existing compositions without regenerating entire images.
Use Cases: Product photo editing | Architectural visualization refinement | E-commerce asset modification
FLUX.1 [pro] Fill operates at competitive inference speeds while maintaining the quality standards of the full FLUX.1 [pro] architecture, with cost scaling directly to output resolution rather than flat per-inference pricing.
| Metric | Result | Context |
|---|
| Cost per Megapixel | $0.05 | Billed by rounding up to nearest megapixel |
| Output Range | 1-4 images | Single API call supports batch generation |
| Safety Tolerance | 6 levels (1-6) | Configurable content moderation strictness |
| Output Formats | JPEG, PNG | Standard web-optimized formats |
| Related Endpoints | FLUX.1 Kontext [pro], FLUX.1 Kontext [max] | Context-aware variants for multi-reference workflows |
Precision Inpainting Without Full Regeneration
FLUX.1 [pro] Fill operates through mask-based editing rather than full image regeneration, requiring three inputs: your base image, a mask defining the edit region, and a text prompt describing the desired fill content. This approach preserves everything outside the mask untouched while applying FLUX.1 [pro]'s generation quality only where needed.
What this means for you:
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Surgical precision: Modify specific objects or regions without risking changes to surrounding elements, critical for product photography where brand consistency matters
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Dual-input control: Mask URL and image URL parameters enable programmatic workflows where masks are generated separately (edge detection, object segmentation, manual selection tools)
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Prompt enhancement option: Optional enhance_prompt parameter applies FLUX's prompt optimization to your instructions, improving interpretation of complex editing requests
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Batch efficiency: Generate up to 4 variations per API call with different seeds, useful for A/B testing edits or exploring alternative fills for the same masked region
Technical Specifications
| Spec | Details |
|---|
| Architecture | FLUX.1 [pro] |
| Input Formats | Image URL (JPEG, PNG, WebP, GIF, AVIF) + Mask URL (matching dimensions) |
| Output Formats | JPEG, PNG |
| Resolution Handling | Variable (billed per megapixel, rounded up) |
| License | Commercial use permitted via fal partnership |
API Documentation | Quickstart Guide | Enterprise Pricing
How It Stacks Up
FLUX.1 Kontext [pro] ($0.055/MP) – FLUX.1 [pro] Fill ($0.05/MP) focuses on single-mask inpainting with straightforward prompt-based fills at 9% lower cost. FLUX.1 Kontext [pro] adds multi-reference image conditioning via URL arrays, enabling style transfer and context-aware fills for workflows requiring visual examples beyond text prompts.
FLUX.1 Kontext [max] ($0.11/MP) – FLUX.1 [pro] Fill delivers core inpainting functionality at 55% lower cost ($0.05 vs $0.11 per megapixel). FLUX.1 Kontext [max] trades cost efficiency for maximum quality output and enhanced multi-reference capabilities, ideal for high-end commercial work where generation fidelity justifies premium pricing.
fal-ai/flux-pro/v1/fill
