Nano Banana 2

Single-file CLI for generating images with Google's Gemini 3.1 Flash model. Supports text-to-image, image-to-image, batch generation with parallel API calls, and automatic grid composition.

Setup

Requires Python 3.13+ and a Gemini API key.

export GEMINI_API_KEY="your-key-here"

Dependencies (requests, pillow) are declared inline via PEP 723 — uv run handles them automatically.

Usage

# text-to-image
uv run img.py -p "a cat wearing sunglasses"

# prompt from file
uv run img.py -f my-prompt.prompt -o portrait.png

# image-to-image with reference photos
uv run img.py -p "oil painting style" -i photo.jpg -o painting.png

# multiple reference images (shell glob)
uv run img.py -p "blend these" -i in_photos/* -o blended.png

# batch: generate 4 variations in parallel, get a grid
uv run img.py -p "sunset landscape" -n 4 -s 2K -a 16:9 -o sunset.png
# → sunset-1.png, sunset-2.png, sunset-3.png, sunset-4.png, sunset.png (grid)

Options

Flag	Description	Default
-p, --prompt	Prompt text	—
-f, --prompt-file	Read prompt from file	—
-i, --input	Reference image(s), repeatable	none
-o, --out	Output filename	output.png
-n, --num-images	Number of images to generate in parallel	1
-s, --size	Resolution: 512px, 1K, 2K, 4K	1K
-a, --aspect-ratio	Aspect ratio (e.g. 16:9, 3:2, 9:16)	API default

Batch output

When -n is greater than 1, individual images are written as <name>-1.png, <name>-2.png, etc. A grid image combining all results is saved to the base output name. The grid uses shelf-packing at original resolution — no resizing or cropping.

Viewer

Open viewer.html in a browser to live-monitor generation progress. It auto-refreshes and displays output images in a grid.