Gemini image API quickstart: Generate Nano Banana images with CometAPI

curl -s -X POST \
  "https://api.cometapi.com/v1beta/models/gemini-3.1-flash-image-preview:generateContent" \
  -H "x-goog-api-key: $COMETAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [
      {
        "parts": [
          {
            "text": "A Monarch butterfly anatomical sketch on textured parchment"
          }
        ]
      }
    ],
    "generationConfig": {
      "responseModalities": ["TEXT", "IMAGE"],
      "imageConfig": {
        "aspectRatio": "1:1",
        "imageSize": "4K"
      }
    }
  }'

import base64
import os
import requests

response = requests.post(
    "https://api.cometapi.com/v1beta/models/gemini-3.1-flash-image-preview:generateContent",
    headers={
        "x-goog-api-key": os.environ["COMETAPI_KEY"],
        "Content-Type": "application/json",
    },
    json={
        "contents": [
            {
                "parts": [
                    {
                        "text": "A Monarch butterfly anatomical sketch on textured parchment"
                    }
                ]
            }
        ],
        "generationConfig": {
            "responseModalities": ["TEXT", "IMAGE"],
            "imageConfig": {"aspectRatio": "1:1", "imageSize": "4K"},
        },
    },
    timeout=120,
)
response.raise_for_status()

parts = response.json()["candidates"][0]["content"]["parts"]
for part in reversed(parts):
    if part.get("thought") is True:
        continue
    inline_data = part.get("inlineData")
    if inline_data:
        image_bytes = base64.b64decode(inline_data["data"])
        mime_type = inline_data.get("mimeType", "image/png")
        extension = "jpg" if mime_type == "image/jpeg" else "png"
        with open(f"nano-banana-result.{extension}", "wb") as file:
            file.write(image_bytes)
        break
else:
    raise RuntimeError("No final image part found")

import fs from "node:fs/promises";

const response = await fetch(
  "https://api.cometapi.com/v1beta/models/gemini-3.1-flash-image-preview:generateContent",
  {
    method: "POST",
    headers: {
      "x-goog-api-key": process.env.COMETAPI_KEY,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      contents: [
        {
          parts: [
            {
              text: "A Monarch butterfly anatomical sketch on textured parchment",
            },
          ],
        },
      ],
      generationConfig: {
        responseModalities: ["TEXT", "IMAGE"],
        imageConfig: { aspectRatio: "1:1", imageSize: "4K" },
      },
    }),
  },
);

if (!response.ok) {
  throw new Error(await response.text());
}

const body = await response.json();
const parts = body.candidates[0].content.parts;
const finalImage = [...parts]
  .reverse()
  .find((part) => part.thought !== true && part.inlineData);

if (!finalImage) {
  throw new Error("No final image part found");
}

const mimeType = finalImage.inlineData.mimeType || "image/png";
const extension = mimeType === "image/jpeg" ? "jpg" : "png";
await fs.writeFile(
  `nano-banana-result.${extension}`,
  Buffer.from(finalImage.inlineData.data, "base64"),
);