Nano Banana Image Generation Skill

Generate and edit images using Google Gemini or OpenAI GPT Image.

Referencing Pasted Images

When images are pasted into Claude Code, they are cached at ~/.claude/image-cache/. Copy from this cache to tmp and use as reference image.

How to Get Image Path (Recommended)

Important: When an image is pasted, always save it to tmp before using.

•User pastes an image
•
Check the image-cache path from Additional working directories in environment info
- •Example: /Users/username/.claude/image-cache/0353f5a1-9885-4743-a956-d2d195b445d4
•Copy the image file from that directory to tmp
•Pass the tmp path to the -r option

Command to Save Image to tmp

bash

# 1. Check image-cache path (from Additional working directories in environment info)
# Example: /Users/username/.claude/image-cache/0353f5a1-9885-4743-a956-d2d195b445d4

# 2. Check images in cache
ls ~/.claude/image-cache/<session-id>/

# 3. Copy to tmp
cp ~/.claude/image-cache/<session-id>/*.png /tmp/reference_image.png

# 4. Use as reference image
python3 ~/.claude/skills/nanobanana/generate.py "Same style. Object: cat" \
  -r "/tmp/reference_image.png" -o cat.png

Example: Generate Using Pasted Image as Reference

bash

# 1. Copy latest image from image-cache to tmp
cp ~/.claude/image-cache/0353f5a1-9885-4743-a956-d2d195b445d4/3.png /tmp/reference_image.png

# 2. Gemini: Copy reference image style
python3 ~/.claude/skills/nanobanana/generate.py "Same style. Object: cat" \
  -r "/tmp/reference_image.png" -o cat.png

# 3. OpenAI: Edit reference image
python3 ~/.claude/skills/nanobanana/generate_openai.py "Change background to night sky" \
  -r "/tmp/reference_image.png" -o edited.png

Legacy Method (When Path is in Metadata)

If image metadata contains [Image: source: /path/to/image.png], use that path directly.

bash

python3 ~/.claude/skills/nanobanana/generate.py "Same style. Object: cat" \
  -r "/Users/user/Desktop/reference.png" -o cat.png

Note: Always wrap paths containing spaces in double quotes.

Pre-generation Confirmation Flow

Important: Before starting image generation, always confirm the following using the AskUserQuestion tool.

Confirmation Items

Common (Always Confirm):

Item	Options	Description
Provider	`gemini` / `openai`	gemini=Nano Banana, openai=GPT Image
Model	Gemini: `pro`/`flash`, OpenAI: `1.5`/`1`/`mini`	See details below
Reference Image	Yes / No	Whether there's a source image to copy style from (pasted images can be used)
Background Removal	Vision API / Magenta removal / OpenAI transparent / Not needed	See methods below

Additional for Multiple Image Generation:

Item	Options	Description
Generation Method	Sheet→split / Parallel generation	Sheet→split recommended (efficient)

Provider Characteristics

Provider	Strengths	API Key Environment Variable
Gemini	Japanese prompts, reference image style copying	`GEMINI_API_KEY`
OpenAI	High quality, native transparent background, multiple simultaneous generation	`OPENAI_API_KEY`

Model Comparison

Gemini:

Model	ID	Features
Flash	`gemini-2.5-flash-image`	Fast, cost-efficient
Pro	`gemini-3-pro-image-preview`	High quality, handles complex instructions

OpenAI:

Model	ID	Features
GPT Image 1.5	`gpt-image-1.5`	Latest & highest quality (recommended)
GPT Image 1	`gpt-image-1`	Standard model
GPT Image Mini	`gpt-image-1-mini`	Lightweight, fast, low cost

Background Removal Method Selection

Method	Best For	Provider
OpenAI Transparent	Use `--background transparent` for direct transparent generation with OpenAI	OpenAI only
Vision API	Real photos, photo-style, complex backgrounds, gradient backgrounds	Gemini
Magenta Removal	Illustrations, simple shapes, line art, flat design	Gemini

Recommended Settings

Case	Provider	Model	Background Removal
Transparent icons/stickers	OpenAI	1.5	`--background transparent`
Reference image style copy	Gemini	pro	Vision API
Simple illustrations	Gemini	flash	Magenta removal
High quality illustrations	OpenAI	1.5	None or transparent
Prototype/testing	OpenAI	mini	None

Tool List

Tool	Description
`generate.py`	Gemini image generation
`generate_openai.py`	OpenAI image generation
`remove-bg-magenta.py`	Magenta background removal (includes 1px erosion)
`remove-bg-vision.py`	Vision API background removal
`erode.py`	Transparent image edge erosion
`split_transparent.py`	Split transparent image into individual objects

Prerequisites

•For Gemini: Set environment variable GEMINI_API_KEY
•For OpenAI: Set environment variable OPENAI_API_KEY
•Vision API: Requires macOS 14.0 (Sonoma) or later

1. generate.py - Gemini Image Generation

bash

python3 ~/.claude/skills/nanobanana/generate.py "prompt" [options]

Options

Option	Description	Default
`-o`, `--output`	Output file path	`generated_image.png`
`-a`, `--aspect-ratio`	Aspect ratio (`1:1`, `16:9`, `9:16`, `4:3`, `3:4`)	`1:1`
`-m`, `--model`	Model (`flash`, `pro`)	`pro`
`--magenta-bg`	Generate with magenta background	None
`-r`, `--reference`	Reference image path	None

Examples

bash

# Simple generation
python3 ~/.claude/skills/nanobanana/generate.py "cute cat illustration"

# Copy reference image style
python3 ~/.claude/skills/nanobanana/generate.py "Same exact style as this image. Object: coffee cup. NO text." -r reference.png -o coffee.png

# Generate with magenta background (for later transparency processing)
python3 ~/.claude/skills/nanobanana/generate.py "simple star icon" --magenta-bg -o star.png

2. generate_openai.py - OpenAI Image Generation

bash

python3 ~/.claude/skills/nanobanana/generate_openai.py "prompt" [options]

Options

Option	Description	Default
`-o`, `--output`	Output file path	`generated_image.png`
`-s`, `--size`	Size (`1024x1024`, `1536x1024`, `1024x1536`, `auto`)	`1024x1024`
`-m`, `--model`	Model (`gpt-image-1`, `gpt-image-1-mini`, `gpt-image-1.5`)	`gpt-image-1.5`
`-q`, `--quality`	Quality (`low`, `medium`, `high`)	`medium`
`-b`, `--background`	Background (`transparent`, `opaque`, `auto`)	`auto`
`-f`, `--format`	Output format (`png`, `jpeg`, `webp`)	`png`
`-r`, `--reference`	Image path to edit	None
`-n`, `--number`	Number of images to generate (1-10)	`1`

Examples

bash

# Simple generation
python3 ~/.claude/skills/nanobanana/generate_openai.py "cute cat illustration"

# Generate with transparent background (no background removal needed)
python3 ~/.claude/skills/nanobanana/generate_openai.py "simple star icon" -b transparent -o star.png

# High quality, landscape
python3 ~/.claude/skills/nanobanana/generate_openai.py "sunset landscape" -s 1536x1024 -q high -o sunset.png

# Generate multiple simultaneously
python3 ~/.claude/skills/nanobanana/generate_openai.py "cute animal icon, single animal" -n 5 -b transparent -o animals.png

# Image editing
python3 ~/.claude/skills/nanobanana/generate_openai.py "change background to night sky" -r input.png -o edited.png

3. remove-bg-magenta.py - Magenta Background Removal

Remove magenta/pink background using color-based detection.

bash

python3 ~/.claude/skills/nanobanana/remove-bg-magenta.py input_image [-o output_image]

How it Works

•Makes colors with R>180, G<100, B>100 transparent
•1px erosion removes pink edge residue

4. remove-bg-vision.py - Vision API Background Removal

Automatically detect and remove background using macOS Vision API.

bash

python3 ~/.claude/skills/nanobanana/remove-bg-vision.py input_image [-o output_image]

Features

•Automatic foreground detection
•Best for images maintaining reference image style (including background)
•Requires macOS 14.0 or later

5. erode.py - Edge Erosion

Erode transparent image edges by specified pixels.

bash

python3 ~/.claude/skills/nanobanana/erode.py input_image [-o output_image] [-i iterations]

Option	Description	Default
`-o`, `--output`	Output image path	Overwrites input
`-i`, `--iterations`	Erosion amount (pixels)	`1`

6. split_transparent.py - Transparent Image Splitting

Split transparent PNG into individual objects (for sticker sheets).

bash

python3 ~/.claude/skills/nanobanana/split_transparent.py input_image [output_directory]

How it Works

•Detects boundaries using alpha channel (transparent areas)
•Extracts each connected component
•Numbers from top-left to bottom-right

Workflow Examples

Generate Using Pasted Image as Reference (Recommended)

When user pastes an image, copy from image-cache to tmp and use as reference.

bash

# 1. Check image-cache path from Additional working directories in environment info
# Example: /Users/username/.claude/image-cache/0353f5a1-9885-4743-a956-d2d195b445d4

# 2. Copy from image-cache to tmp
cp ~/.claude/image-cache/0353f5a1-9885-4743-a956-d2d195b445d4/*.png /tmp/reference_image.png

# 3. Gemini: Generate different object in same style
python3 ~/.claude/skills/nanobanana/generate.py "Same exact style as this image. Object: coffee cup. NO text." \
  -r "/tmp/reference_image.png" -o coffee.png

# 4. OpenAI: Edit image
python3 ~/.claude/skills/nanobanana/generate_openai.py "change background to outer space" \
  -r "/tmp/reference_image.png" -o space.png

OpenAI: Transparent Icon Generation (Recommended - Simplest)

bash

# Generate transparent PNG in one step
python3 ~/.claude/skills/nanobanana/generate_openai.py "simple star icon" -b transparent -o star.png

OpenAI: Multiple Icon Simultaneous Generation

bash

# Generate 5 transparent PNGs simultaneously
python3 ~/.claude/skills/nanobanana/generate_openai.py "cute animal icon, single animal" -n 5 -b transparent -o animal.png
# → animal_01.png, animal_02.png, ... will be generated

Gemini: Transparent Sticker Generation (Simple Objects)

bash

# 1. Generate with magenta background
python3 ~/.claude/skills/nanobanana/generate.py "simple star icon" --magenta-bg -o star.png

# 2. Remove magenta
python3 ~/.claude/skills/nanobanana/remove-bg-magenta.py star.png

Gemini: Reference Image Style Copy + Transparency

bash

# 1. Generate with reference image style (no magenta to maintain style)
python3 ~/.claude/skills/nanobanana/generate.py "Same exact style as this image. Object: coffee cup. NO text." -r reference.png -o coffee.png

# 2. Remove background with Vision API
python3 ~/.claude/skills/nanobanana/remove-bg-vision.py coffee.png

Gemini: Sticker Sheet Generation → Split

bash

# 1. Generate multiple stickers with magenta background
python3 ~/.claude/skills/nanobanana/generate.py \
  "Multiple separate kawaii stickers with LARGE gaps: coffee cup, donut, cat, star. Arranged in 2x2 grid, well separated." \
  --magenta-bg -o sheet.png

# 2. Make background transparent
python3 ~/.claude/skills/nanobanana/remove-bg-magenta.py sheet.png

# 3. Split into individual files
python3 ~/.claude/skills/nanobanana/split_transparent.py sheet.png ./stickers/

Prompt Tips:

•LARGE gaps between them - Wide spacing
•well separated - No overlapping
•Arranged in XxY grid - Specify grid layout

File Structure

code

~/.claude/skills/nanobanana/
├── SKILL.md               # This document
├── generate.py            # Gemini image generation
├── generate_openai.py     # OpenAI image generation
├── remove-bg-magenta.py   # Magenta background removal (includes 1px erosion)
├── remove-bg-vision.py    # Vision API background removal
├── remove-bg.swift        # Vision API implementation (Swift)
├── erode.py               # Edge erosion (standalone)
└── split_transparent.py   # Transparent image splitting