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:

bash

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:

bash

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-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: <subject>. Style: <style>. Composition: <camera/shot>. Lighting: <lighting>. Background: <background>. Color palette: <palette>. Avoid: <list>.”
Editing template (preserve everything else):
- “Change ONLY: <single 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

Examples

Generate new image:

bash

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 4K

Edit existing image:

bash

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

nano-banana-pro

NPX Install

Tags

SKILL.md Content

Nano Banana Pro Image Generation & Editing

Usage

Default Workflow (draft → iterate → final)

Resolution Options

API Key

Preflight + Common Failures (fast fixes)

Filename Generation

Image Editing

Prompt Handling

Prompt Templates (high hit-rate)

Output

Examples