nanobanana2 Image Generation & Editing

Generate new images or edit existing ones using Google's nanobanana2 API (Gemini 3.1 Flash Image preview, model id gemini-3.1-flash-image-preview).

Usage

Run the script using absolute path (do NOT cd to skill directory first):

Generate new image:

uv run "$HOME/.openclaw/skills/skills/nanobanana2/scripts/generate_image.py" --prompt "your image description" --filename "output-name.png" [--resolution 512|1K|2K|4K] [--aspect-ratio RATIO] [--api-key KEY]

Edit existing image:

uv run "$HOME/.openclaw/skills/nanobanana2/scripts/generate_image.py" --prompt "editing instructions" --filename "output-name.png" --input-image "path/to/input.png" [--resolution 512|1K|2K|4K] [--aspect-ratio RATIO] [--api-key KEY]

Important: Always run from the user's current working directory so images are saved where the user is working, not in the skill directory.

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 "$HOME/.openclaw/skills/nanobanana2/scripts/generate_image.py" --prompt "\x3Cdraft prompt>" --filename "yyyy-mm-dd-hh-mm-ss-draft.png" --resolution 1K
• Iterate: adjust prompt in small diffs; keep filename new per run
  • If editing: keep the same --input-image for every iteration until you’re happy.
• Final (4K): only when prompt is locked
  • uv run "$HOME/.openclaw/skills/nanobanana2/scripts/generate_image.py" --prompt "\x3Cfinal prompt>" --filename "yyyy-mm-dd-hh-mm-ss-final.png" --resolution 4K

Resolution (image_size)

nanobanana2 accepts these image_size values (see docs): 512, 1K, 2K, 4K. Use uppercase K for 1K/2K/4K; 512 has no K suffix (smaller output, Flash-only).

• 512 — lowest tier (~512px shortest side per aspect table); good for thumbnails / fastest drafts
• 1K (default) — ~1024px class
• 2K — ~2048px class
• 4K — ~4096px class

Map user requests:

• No mention of resolution → 1K
• "tiny", "thumbnail", "512", "low pixel" → 512
• "low resolution", "1080", "1080p", "1K" → 1K
• "2K", "2048", "normal", "medium resolution" → 2K
• "high resolution", "high-res", "hi-res", "4K", "ultra" → 4K

Aspect ratio (aspect_ratio)

Optional. If omitted, the API defaults apply (e.g. 1:1 for pure text-to-image, or match input image when editing — per API behavior).

Supported values for Gemini 3.1 Flash Image: 1:1, 1:4, 1:8, 2:3, 3:2, 3:4, 4:1, 4:3, 4:5, 5:4, 8:1, 9:16, 16:9, 21:9.

Pass explicitly when the user asks for wallpaper, story, reel, banner, etc., e.g. --aspect-ratio 9:16 or --aspect-ratio 16:9.

API Key

The script checks for API key in this order:

1. --api-key argument (use if user provided key in chat)
2. GEMINI_API_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 \"$GEMINI_API_KEY\" (or pass --api-key)
  • If editing: test -f \"path/to/input.png\"

• Common failures:

  • Error: No API key provided. → set GEMINI_API_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: \x3Csubject>. Style: \x3Cstyle>. Composition: \x3Ccamera/shot>. Lighting: \x3Clighting>. Background: \x3Cbackground>. Color palette: \x3Cpalette>. Avoid: \x3Clist>.”

• Editing template (preserve everything else):

  • “Change ONLY: \x3Csingle change>. Keep identical: subject, composition/crop, pose, lighting, color palette, background, text, and overall style. Do not add new objects. If text exists, keep it unchanged.”

Output

• Saves PNG to current directory (or specified path if filename includes directory)

• Script outputs the full path to the generated image

• Do not read the image back - just inform the user of the saved path

• Generated images include SynthID watermark (API policy).

Examples

Generate new image:

uv run "$HOME/.openclaw/skills/nanobanana2/scripts/generate_image.py" --prompt "A serene Japanese garden with cherry blossoms" --filename "2025-11-23-14-23-05-japanese-garden.png" --resolution 4K --aspect-ratio 16:9

Edit existing image:

uv run "$HOME/.openclaw/skills/nanobanana2/scripts/generate_image.py" --prompt "make the sky more dramatic with storm clouds" --filename "2025-11-23-14-25-30-dramatic-sky.png" --input-image "original-photo.jpg" --resolution 2K