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:
CODEBLOCK0
Edit existing image:
CODEBLOCK1
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
- INLINECODE2
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 → INLINECODE3
- "low resolution", "1080", "1080p", "1K" → INLINECODE4
- "2K", "2048", "normal", "medium resolution" → INLINECODE5
- "high resolution", "high-res", "hi-res", "4K", "ultra" → INLINECODE6
API Key
The script checks for API key in this order:
- 1.
--api-key argument (use if user provided key in chat) - INLINECODE8 environment variable
If neither is available, the script exits with an error message.
Preflight + Common Failures (fast fixes)
-
command -v uv (must exist)
-
test -n \"$GEMINI_API_KEY\" (or pass
--api-key)
- If editing: INLINECODE12
-
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: INLINECODE18
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" → INLINECODE23
- Prompt "sunset over mountains" → INLINECODE24
- Prompt "create an image of a robot" → INLINECODE25
- Unclear context → INLINECODE26
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
- 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.
- “Create an image of:
. Style: