Nano Banana Pro Image Generation & Editing

Generate new images or edit existing ones using Google's Nano Banana Pro API (Gemini 3 Pro Image).

Usage

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

Generate new image:

uv run ~/.codex/skills/nano-banana-pro/scripts/generate_image.py --prompt "your image description" --filename "output-name.png" [--resolution 1K|2K|4K] [--api-key KEY]

Edit existing image:

uv run ~/.codex/skills/nano-banana-pro/scripts/generate_image.py --prompt "editing instructions" --filename "output-name.png" --input-image "path/to/input.png" [--resolution 1K|2K|4K] [--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 ~/.codex/skills/nano-banana-pro/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 ~/.codex/skills/nano-banana-pro/scripts/generate_image.py --prompt "" --filename "yyyy-mm-dd-hh-mm-ss-final.png" --resolution 4K

Resolution Options

The Gemini 3 Pro Image 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:

--api-key argument (use if user provided key in chat)

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:

Check if they provide an image path or reference an image in the current directory

Use --input-image parameter with the path to the image

The prompt should contain editing instructions (e.g., "make the sky more dramatic", "remove the person", "change to cartoon style")

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: