feat: SOTA AI photo colorization with DDColor deep learning model (#57) (#58)

Add AI-powered photo colorization that converts B&W/grayscale images to
full color using DDColor (ICCV 2023 dual-decoder architecture) via ONNX
Runtime. Includes model selection (Auto/DDColor/Classic), adjustable color
intensity, batch processing, before/after preview, and full HEIC/HEIF support.

Co-authored-by: stirling-image <stirling-image@users.noreply.github.com>

packages/ai/src/colorization.ts

@@ -0,0 +1,46 @@
+import { readFile, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { type ProgressCallback, runPythonWithProgress } from "./bridge.js";
+
+export interface ColorizeOptions {
+  intensity?: number;
+  model?: string;
+}
+
+export interface ColorizeResult {
+  buffer: Buffer;
+  width: number;
+  height: number;
+  method: string;
+}
+
+export async function colorize(
+  inputBuffer: Buffer,
+  outputDir: string,
+  options: ColorizeOptions = {},
+  onProgress?: ProgressCallback,
+): Promise<ColorizeResult> {
+  const inputPath = join(outputDir, "input_colorize.png");
+  const outputPath = join(outputDir, "output_colorize.png");
+
+  await writeFile(inputPath, inputBuffer);
+  const { stdout } = await runPythonWithProgress(
+    "colorize.py",
+    [inputPath, outputPath, JSON.stringify(options)],
+    { onProgress },
+  );
+
+  const result = JSON.parse(stdout);
+  if (!result.success) {
+    throw new Error(result.error || "Colorization failed");
+  }
+
+  const actualOutputPath = result.output_path || outputPath;
+  const buffer = await readFile(actualOutputPath);
+  return {
+    buffer,
+    width: result.width,
+    height: result.height,
+    method: result.method ?? "unknown",
+  };
+}

packages/ai/src/index.ts

@@ -1,5 +1,6 @@
 export { removeBackground } from "./background-removal.js";
 export { isGpuAvailable, shutdownDispatcher } from "./bridge.js";
+export { colorize } from "./colorization.js";
 export type { DetectFacesResult, FaceRegion } from "./face-detection.js";
 export { blurFaces, detectFaces } from "./face-detection.js";
 export { inpaint } from "./inpainting.js";