alterlab-generate-image

Generate Image

Generate and edit high-quality images using OpenRouter's image generation models including FLUX.2 Pro and Gemini 3.1 Flash Image (a.k.a. "Nano Banana 2").

When to Use This Skill

Use this skill (alterlab-generate-image) for:

• Photos and photorealistic images
• Artistic illustrations and artwork
• Concept art and visual concepts
• Visual assets for presentations or documents
• Image editing and modifications
• Any general-purpose image generation needs

Does NOT Trigger

Scenario	Use Instead
Flowchart, CONSORT/PRISMA or methodology diagram, circuit, biological pathway, system or neural-network architecture	alterlab-scientific-schematics
Infographic that lays out statistics, a timeline, a comparison, or process steps as a designed graphic	alterlab-infographics
Plot of numeric data from a file or array (scatter, bar, line, distribution)	alterlab-matplotlib / alterlab-seaborn / alterlab-plotly
Diagram that should stay editable, version-controlled text in a README or Markdown doc	alterlab-mermaid

Quick Start

Use the scripts/generate_image.py script to generate or edit images:

# Generate a new image
python scripts/generate_image.py "A beautiful sunset over mountains"

# Edit an existing image
python scripts/generate_image.py "Make the sky purple" --input photo.jpg

This generates/edits an image and saves it as generated_image.png in the current directory.

API Key Setup

The script needs an OpenRouter API key and stops with an error if it can't find one. It checks, in order: the --api-key flag, the OPENROUTER_API_KEY environment variable, then an OPENROUTER_API_KEY=<key> line in a .env file in the current or a parent directory. If none is set, ask the user to either:

• export OPENROUTER_API_KEY=your-api-key-here, or
• add OPENROUTER_API_KEY=your-api-key-here to a .env file.

Keys are issued at https://openrouter.ai/keys.

Data & Privacy

This skill sends your prompts and any input image to a third-party API (OpenRouter) for processing. Avoid sending confidential, clinical, or unpublished material. The OpenRouter API key is read from the environment (OPENROUTER_API_KEY).

Model Selection

Default: google/gemini-3.1-flash-image ("Nano Banana 2", GA) — high quality, generation + editing. Use this unless there's a reason not to. It replaced google/gemini-3.1-flash-image-preview, which Google shut down on 2026-06-25. Set ALTERLAB_IMAGE_MODEL to change the default for every run, or pass --model for one run.

Other models (all support both generation and editing on OpenRouter):

• black-forest-labs/flux.2-pro — frontier visual quality, strong prompt adherence, up to 4 MP.
• black-forest-labs/flux.2-flex — cheaper; especially good at rendering text/typography and fine detail.

Model IDs are version-sensitive (verified against the OpenRouter model list on 2026-09-23) — re-check https://openrouter.ai/models if a call returns a "model not found" error. The script uses OpenRouter's chat-completions endpoint with the modalities parameter. OpenRouter launched a dedicated Image API (/api/v1/images) in June 2026: image models that existed then stay available on chat completions (all models listed here do), but models added since may be served only by the Image API — if a newer model fails with this script, that is the likely reason.

Common Usage Patterns

# Generate (default model) to a chosen path
python scripts/generate_image.py "Abstract art" --output artwork.png

# Generate with a specific model
python scripts/generate_image.py "A cat in space" --model "black-forest-labs/flux.2-pro"

# Edit an existing image (edit mode is triggered by --input)
python scripts/generate_image.py "Add sunglasses to the person" --input portrait.png --output cleaned.png

For multiple images, run the script once per prompt with distinct --output paths (it always writes one file and overwrites the default generated_image.png).

Script Parameters

• prompt (required): Text description of the image to generate, or editing instructions
• --input or -i: Input image path for editing (enables edit mode)
• --model or -m: OpenRouter model ID (default: $ALTERLAB_IMAGE_MODEL, else google/gemini-3.1-flash-image)
• --output or -o: Output file path (default: generated_image.png)
• --api-key: OpenRouter API key (overrides OPENROUTER_API_KEY and .env)

Example Use Cases

# Conceptual figure for a paper (illustration, not a data plot)
python scripts/generate_image.py "Microscopic view of cancer cells being attacked by immunotherapy agents, clean scientific illustration style" --output figures/immunotherapy_concept.png

# Slide background / poster hero image
python scripts/generate_image.py "Abstract blue and white background with subtle molecular patterns, professional presentation style" --output slides/background.png
python scripts/generate_image.py "Modern, well-lit laboratory with current equipment, photorealistic" --output poster/hero.png

Notes & Tips

• Output is always one PNG. Images come back base64-encoded (as a data URL or content part) and are decoded and written to --output; the script handles both the images and content response shapes used by different OpenRouter models.
• Supported input formats for editing: PNG, JPEG, GIF, WebP. The input is base64-encoded and sent with the edit prompt.
• Editing works best with specific, element-referenced instructions — "change the sky to sunset colors" beats "edit the sky".
• Generation typically takes ~5-30 s depending on model. Pricing: https://openrouter.ai/models
• The script exits non-zero with a clear message on a missing API key, missing requests, a network error, an API error (with status code), or a response without an image — read it and fix before retrying.
• If an image-only model (e.g. FLUX.2) rejects the request with a 400/422, the script retries once asking for image output only.