nanobanana-openrouter

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name: nano-banana-pro description: Generate/edit images with Nano Banana Pro (Gemini 3 Pro Image) via OpenRouter. Use for image create/modify requests incl. edits. Supports text-to-image + image-to-image; 1K/2K/4K; use --input-image.

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Nano Banana Pro Image Generation & Editing

Generate new images or edit existing ones using OpenRouter (model: google/gemini-3-pro-image-preview).

Usage

Run the script using absolute path:

Generate new image:

uv run /path/to/this/skill/scripts/generate_image.py --prompt "your image description" --filename "output-name.png" [--resolution 1K|2K|4K] [--api-key KEY]

Edit existing image:

uv run /path/to/this/skill/scripts/generate_image.py --prompt "editing instructions" --filename "output-name.png" --input-image "path/to/input.png" [--resolution 1K|2K|4K] [--api-key KEY]

Custom output directory:

uv run /path/to/this/skill/scripts/generate_image.py --prompt "your image description" --filename "output-name.png" --output-dir "/custom/path"

Output Location:

Default: Images are saved to ./output_images/ (relative to this skill's root directory)

Custom: Use --output-dir to specify a different directory

The script will create the output directory if it doesn't exist

Default Workflow (draft → iterate → final)

Goal: fast iteration without burning time on 4K until the prompt is correct.

Draft (1K): quick feedback loop

- uv run /path/to/this/skill/scripts/generate_image.py --prompt "" --filename "yyyy-mm-dd-hh-mm-ss-draft.png" --resolution 1K

Iterate: adjust prompt in small diffs; keep filename new per run

- If editing: keep the same --input-image for every iteration until you’re happy.

Final (4K): only when prompt is locked

- uv run /path/to/this/skill/scripts/generate_image.py --prompt "" --filename "yyyy-mm-dd-hh-mm-ss-final.png" --resolution 4K

Resolution Options

The OpenRouter API supports three resolutions (uppercase K required):

1K (default) - ~1024px resolution

2K - ~2048px resolution

4K - ~4096px resolution

Map user requests to API parameters:

No mention of resolution → 1K

"low resolution", "1080", "1080p", "1K" → 1K

"2K", "2048", "normal", "medium resolution" → 2K

"high resolution", "high-res", "hi-res", "4K", "ultra" → 4K

API Key

The script checks for API key in this order: 1. --api-key argument (use if user provided key in chat) 2. OPENROUTER_KEY environment variable

If neither is available, the script exits with an error message.

Preflight + Common Failures (fast fixes)

Preflight:

- command -v uv (must exist) - test -n \"$OPENROUTER_KEY\" (or pass --api-key) - If editing: test -f \"path/to/input.png\"

Common failures:

- Error: No API key provided. → set OPENROUTER_KEY or pass --api-key - Error loading input image: → wrong path / unreadable file; verify --input-image points to a real image - “quota/permission/403” style API errors → wrong key, no access, or quota exceeded; try a different key/account

Filename Generation

Generate filenames with the pattern: yyyy-mm-dd-hh-mm-ss-name.png

Format: {timestamp}-{descriptive-name}.png

Timestamp: Current date/time in format yyyy-mm-dd-hh-mm-ss (24-hour format)

Name: Descriptive lowercase text with hyphens

Keep the descriptive part concise (1-5 words typically)

Use context from user's prompt or conversation

If unclear, use random identifier (e.g., x9k2, a7b3)

Examples:

Prompt "A serene Japanese garden" → 2025-11-23-14-23-05-japanese-garden.png

Prompt "sunset over mountains" → 2025-11-23-15-30-12-sunset-mountains.png

Prompt "create an image of a robot" → 2025-11-23-16-45-33-robot.png

Unclear context → 2025-11-23-17-12-48-x9k2.png

Image Editing

When the user wants to modify an existing image: 1. Check if they provide an image path or reference an image in the current directory 2. Use --input-image parameter with the path to the image 3. The prompt should contain editing instructions (e.g., "make the sky more dramatic", "remove the person", "change to cartoon style") 4. Common editing tasks: add/remove elements, change style, adjust colors, blur background, etc.

Prompt Handling

For generation: Pass user's image description as-is to --prompt. Only rework if clearly insufficient.

For editing: Pass editing instructions in --prompt (e.g., "add a rainbow in the sky", "make it look like a watercolor painting")

Preserve user's creative intent in both cases.

Prompt Templates (high hit-rate)

Use templates when the user is vague or when edits must be precise.

Generation template:

- “Create an image of: . Style: