gen_image_prompt_only.py

#!/usr/bin/env python3
import argparse
import json
import os
import sys
import threading
import time
from pathlib import Path

from google import genai
from google.genai import types


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description="Generate an image from a text prompt using Gemini (Nano Banana)."
    )
    parser.add_argument("--prompt", required=True, help="Prompt describing the image.")
    parser.add_argument(
        "--model",
        default="gemini-3.1-flash-image-preview",
        help="Image generation model name (e.g. gemini-3.1-flash-image-preview, gemini-3-pro-image-preview, gemini-2.5-flash-image).",
    )
    parser.add_argument("--name", default="generated_image", help="Base output filename (without extension).")
    parser.add_argument(
        "--output-dir",
        "--output_dir",
        dest="output_dir",
        default="output_dir",
        help="Directory to save outputs (default: output_dir).",
    )
    parser.add_argument(
        "--aspect-ratio",
        default="1:1",
        help="Aspect ratio (e.g. 1:1, 16:9, 9:16, 4:3, 3:4, 21:9).",
    )
    parser.add_argument(
        "--resolution",
        default="1K",
        help="Output resolution: 512px, 1K, 2K, or 4K (Gemini 3 models only).",
    )
    parser.add_argument(
        "--number-of-images",
        type=int,
        default=1,
        help="How many images to generate (runs the request N times).",
    )
    parser.add_argument(
        "--thinking-level",
        default=None,
        choices=["minimal", "high"],
        help="Thinking level for Gemini 3.1 Flash Image: 'minimal' or 'high'.",
    )
    return parser.parse_args()


def build_image_config(args: argparse.Namespace) -> types.ImageConfig:
    kwargs: dict = {"aspect_ratio": args.aspect_ratio}
    image_models_with_size = {
        "gemini-2.5-flash-image",
        "gemini-3.1-flash-image-preview",
        "gemini-3-pro-image-preview",
    }
    if args.model in image_models_with_size:
        kwargs["image_size"] = args.resolution
    return types.ImageConfig(**kwargs)


def generate_one(
    client: genai.Client,
    args: argparse.Namespace,
    image_config: types.ImageConfig,
) -> bytes | None:
    config_kwargs: dict = {
        "response_modalities": ["IMAGE"],
        "image_config": image_config,
    }
    if args.thinking_level and args.model == "gemini-3.1-flash-image-preview":
        config_kwargs["thinking_config"] = types.ThinkingConfig(
            thinking_level=args.thinking_level.capitalize(),
        )

    response = client.models.generate_content(
        model=args.model,
        contents=[args.prompt],
        config=types.GenerateContentConfig(**config_kwargs),
    )

    for part in response.parts:
        if part.thought:
            continue
        if part.inline_data is not None:
            return part.inline_data.data

    return None


def main() -> int:
    args = parse_args()

    if not os.getenv("GEMINI_API_KEY"):
        print("Missing GEMINI_API_KEY environment variable.", file=sys.stderr)
        return 1

    client = genai.Client()
    image_config = build_image_config(args)

    out_dir = Path(args.output_dir)
    out_dir.mkdir(parents=True, exist_ok=True)

    saved_files: list[str] = []

    for idx in range(1, args.number_of_images + 1):
        label = f" ({idx}/{args.number_of_images})" if args.number_of_images > 1 else ""
        print(f"Generating image{label}...")

        result: dict = {}
        thread = threading.Thread(
            target=lambda: result.update({"bytes": generate_one(client, args, image_config)}),
            daemon=True,
        )
        started_at = time.time()
        thread.start()
        while thread.is_alive():
            thread.join(timeout=10)
            if thread.is_alive():
                elapsed = int(time.time() - started_at)
                print(f"Waiting for image generation... elapsed: {elapsed}s")
        elapsed = int(time.time() - started_at)
        print(f"Image generation finished in {elapsed}s")

        image_bytes = result.get("bytes")
        if image_bytes is None:
            print(f"No image returned for generation {idx}.", file=sys.stderr)
            continue

        if args.number_of_images == 1:
            out_path = out_dir / f"{args.name}.png"
        else:
            out_path = out_dir / f"{args.name}_{idx}.png"

        out_path.write_bytes(image_bytes)
        saved_files.append(str(out_path.resolve()))
        print(f"Saved image: {out_path.resolve()}")

    if not saved_files:
        print("No images were saved.", file=sys.stderr)
        return 2

    metadata: dict = {
        "prompt": args.prompt,
        "model": args.model,
        "config": {
            "aspect_ratio": args.aspect_ratio,
            "resolution": args.resolution,
            "number_of_images": args.number_of_images,
            "thinking_level": args.thinking_level,
        },
        "saved_images": saved_files,
    }
    metadata_path = out_dir / f"{args.name}.json"
    metadata_path.write_text(json.dumps(metadata, indent=2), encoding="utf-8")
    print(f"Saved metadata: {metadata_path.resolve()}")

    return 0


if __name__ == "__main__":
    raise SystemExit(main())