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 "<draft 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 "<final 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-keyargument (use if user provided key in chat)GEMINI_API_KEYenvironment 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-imageparameter 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:. Composition: <camera/shot>. Lighting:. Background:. Color palette:. Avoid:.”
- Editing template (preserve everything else):
- “Change ONLY:. 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
Examples
Generate new image:
uv run ~/.codex/skills/nano-banana-pro/scripts/generate_image.py --prompt "A serene Japanese garden with cherry blossoms" --filename "2025-11-23-14-23-05-japanese-garden.png" --resolution 4KEdit existing image:
uv run ~/.codex/skills/nano-banana-pro/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