feat(gemini-web): auto-remove watermark from generated images

Uses reverse alpha blending to restore original pixels from Gemini's
visible watermark. Enabled by default; opt out with --keep-watermark.
Algorithm ported from gemini-watermark-remover (MIT).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/baoyu-danger-gemini-web/SKILL.md

@@ -122,10 +122,19 @@ ${BUN_X} {baseDir}/scripts/main.ts "Hello" --json
 | `--sessionId` | Session ID for multi-turn conversation |
 | `--list-sessions` | List saved sessions |
 | `--json` | Output as JSON |
+| `--keep-watermark` | Skip watermark removal (removed by default) |
 | `--login` | Refresh cookies, then exit |
 | `--cookie-path` | Custom cookie file path |
 | `--profile-dir` | Chrome profile directory |
 
+## Watermark Removal
+
+Generated images have Gemini's visible watermark removed by default using reverse alpha blending. This is a lossless mathematical operation that precisely restores the original pixels — not AI inpainting.
+
+To keep the watermark, pass `--keep-watermark`.
+
+Algorithm credit: [gemini-watermark-remover](https://github.com/journey-ad/gemini-watermark-remover) by journey-ad, based on [GeminiWatermarkTool](https://github.com/allenk/GeminiWatermarkTool) by allenk.
+
 ## Models
 
 | Model | Description |

skills/baoyu-danger-gemini-web/scripts/bun.lock

@@ -5,10 +5,22 @@
       "name": "baoyu-danger-gemini-web-scripts",
       "dependencies": {
         "baoyu-chrome-cdp": "file:./vendor/baoyu-chrome-cdp",
+        "pngjs": "^7.0.0",
+      },
+      "devDependencies": {
+        "@types/pngjs": "^6.0.5",
       },
     },
   },
   "packages": {
+    "@types/node": ["@types/node@25.5.0", "", { "dependencies": { "undici-types": "~7.18.0" } }, "sha512-jp2P3tQMSxWugkCUKLRPVUpGaL5MVFwF8RDuSRztfwgN1wmqJeMSbKlnEtQqU8UrhTmzEmZdu2I6v2dpp7XIxw=="],
+
+    "@types/pngjs": ["@types/pngjs@6.0.5", "", { "dependencies": { "@types/node": "*" } }, "sha512-0k5eKfrA83JOZPppLtS2C7OUtyNAl2wKNxfyYl9Q5g9lPkgBl/9hNyAu6HuEH2J4XmIv2znEpkDd0SaZVxW6iQ=="],
+
     "baoyu-chrome-cdp": ["baoyu-chrome-cdp@file:vendor/baoyu-chrome-cdp", {}],
+
+    "pngjs": ["pngjs@7.0.0", "", {}, "sha512-LKWqWJRhstyYo9pGvgor/ivk2w94eSjE3RGVuzLGlr3NmD8bf7RcYGze1mNdEHRP6TRP6rMuDHk5t44hnTRyow=="],
+
+    "undici-types": ["undici-types@7.18.2", "", {}, "sha512-AsuCzffGHJybSaRrmr5eHr81mwJU3kjw6M+uprWvCXiNeN9SOGwQ3Jn8jb8m3Z6izVgknn1R0FTCEAP2QrLY/w=="],
   }
 }

skills/baoyu-danger-gemini-web/scripts/gemini-webapi/types/image.ts

@@ -3,6 +3,7 @@ import { mkdir, writeFile } from 'node:fs/promises';
 
 import { logger } from '../utils/logger.js';
 import { cookie_header, fetch_with_timeout } from '../utils/http.js';
+import { removeWatermarkFromFile } from '../watermark.js';
 
 export class Image {
   constructor(
@@ -105,10 +106,20 @@ export class GeneratedImage extends Image {
     verbose: boolean = false,
     skip_invalid_filename: boolean = false,
     full_size: boolean = true,
+    stripWatermark: boolean = true,
   ): Promise<string | null> {
     const u = full_size ? `${this.url}=s2048` : this.url;
     const f = filename ?? `${new Date().toISOString().replace(/[-:.TZ]/g, '').slice(0, 14)}_${u.slice(-10)}.png`;
     const img = new Image(u, this.title, this.alt, this.proxy);
-    return await img.save(p, f, cookies ?? this.cookies, verbose, skip_invalid_filename);
+    const dest = await img.save(p, f, cookies ?? this.cookies, verbose, skip_invalid_filename);
+    if (dest && stripWatermark) {
+      try {
+        const removed = await removeWatermarkFromFile(dest);
+        if (verbose) logger.info(removed ? `Watermark removed from ${dest}` : `Watermark removal skipped (non-PNG?) for ${dest}`);
+      } catch (e) {
+        if (verbose) logger.warning(`Watermark removal failed: ${e}`);
+      }
+    }
+    return dest;
   }
 }

skills/baoyu-danger-gemini-web/scripts/gemini-webapi/watermark.ts

@@ -0,0 +1,95 @@
+import path from 'node:path';
+import { readFile, writeFile } from 'node:fs/promises';
+import { PNG } from 'pngjs';
+
+const ALPHA_THRESHOLD = 0.002;
+const MAX_ALPHA = 0.99;
+const LOGO_VALUE = 255;
+
+type WmConfig = { logoSize: number; marginRight: number; marginBottom: number };
+type WmPosition = { x: number; y: number; width: number; height: number };
+
+function detectConfig(w: number, h: number): WmConfig {
+  if (w > 1024 && h > 1024) return { logoSize: 96, marginRight: 64, marginBottom: 64 };
+  return { logoSize: 48, marginRight: 32, marginBottom: 32 };
+}
+
+function calcPosition(w: number, h: number, cfg: WmConfig): WmPosition {
+  return {
+    x: w - cfg.marginRight - cfg.logoSize,
+    y: h - cfg.marginBottom - cfg.logoSize,
+    width: cfg.logoSize,
+    height: cfg.logoSize,
+  };
+}
+
+function buildAlphaMap(bgData: Buffer, w: number, h: number): Float32Array {
+  const map = new Float32Array(w * h);
+  for (let i = 0; i < map.length; i++) {
+    const idx = i * 4;
+    map[i] = Math.max(bgData[idx]!, bgData[idx + 1]!, bgData[idx + 2]!) / 255.0;
+  }
+  return map;
+}
+
+function applyReverseBlend(
+  data: Buffer,
+  imgW: number,
+  alphaMap: Float32Array,
+  pos: WmPosition,
+): void {
+  for (let row = 0; row < pos.height; row++) {
+    for (let col = 0; col < pos.width; col++) {
+      const imgIdx = ((pos.y + row) * imgW + (pos.x + col)) * 4;
+      const alphaIdx = row * pos.width + col;
+      let alpha = alphaMap[alphaIdx]!;
+
+      if (alpha < ALPHA_THRESHOLD) continue;
+      alpha = Math.min(alpha, MAX_ALPHA);
+      const inv = 1.0 - alpha;
+
+      for (let c = 0; c < 3; c++) {
+        const val = (data[imgIdx + c]! - alpha * LOGO_VALUE) / inv;
+        data[imgIdx + c] = Math.max(0, Math.min(255, Math.round(val)));
+      }
+    }
+  }
+}
+
+const alphaMaps: Record<number, Float32Array> = {};
+
+async function getAlphaMap(size: number): Promise<Float32Array> {
+  if (alphaMaps[size]) return alphaMaps[size]!;
+
+  const file = size === 48 ? 'bg_48.png' : 'bg_96.png';
+  const dir = (import.meta as any).dir ?? path.dirname(new URL(import.meta.url).pathname);
+  const buf = await readFile(path.join(dir, 'assets', file));
+  const png = PNG.sync.read(buf);
+  const map = buildAlphaMap(png.data as unknown as Buffer, png.width, png.height);
+  alphaMaps[size] = map;
+  return map;
+}
+
+export async function removeWatermarkFromFile(filePath: string): Promise<boolean> {
+  const buf = await readFile(filePath);
+
+  let png: PNG;
+  try {
+    png = PNG.sync.read(buf);
+  } catch {
+    return false;
+  }
+
+  const { width, height } = png;
+  const cfg = detectConfig(width, height);
+  const pos = calcPosition(width, height, cfg);
+
+  if (pos.x < 0 || pos.y < 0) return false;
+
+  const alphaMap = await getAlphaMap(cfg.logoSize);
+  applyReverseBlend(png.data as unknown as Buffer, width, alphaMap, pos);
+
+  const out = PNG.sync.write(png);
+  await writeFile(filePath, out);
+  return true;
+}

skills/baoyu-danger-gemini-web/scripts/main.ts

@@ -18,6 +18,7 @@ type CliArgs = {
   login: boolean;
   cookiePath: string | null;
   profileDir: string | null;
+  keepWatermark: boolean;
   help: boolean;
 };
 
@@ -95,6 +96,7 @@ Options:
   --ref <files...>          Alias for --reference
   --sessionId <id>          Session ID for multi-turn conversation (agent should generate unique ID)
   --list-sessions           List saved sessions (max 100, sorted by update time)
+  --keep-watermark          Skip watermark removal (watermark is removed by default)
   --login                   Only refresh cookies, then exit
   --cookie-path <path>      Cookie file path (default: ${cookiePath})
   --profile-dir <path>      Chrome profile dir (default: ${profileDir})
@@ -117,6 +119,7 @@ function parseArgs(argv: string[]): CliArgs {
     login: false,
     cookiePath: null,
     profileDir: null,
+    keepWatermark: false,
     help: false,
   };
 
@@ -157,6 +160,11 @@ function parseArgs(argv: string[]): CliArgs {
       continue;
     }
 
+    if (a === '--keep-watermark') {
+      out.keepWatermark = true;
+      continue;
+    }
+
     if (a === '--prompt' || a === '-p') {
       const v = argv[++i];
       if (!v) throw new Error(`Missing value for ${a}`);
@@ -474,7 +482,7 @@ async function main(): Promise<void> {
       const dp = dir;
 
       if (img instanceof GeneratedImage) {
-        savedImage = await img.save(dp, fn, undefined, false, false, true);
+        savedImage = await img.save(dp, fn, undefined, false, false, true, !args.keepWatermark);
       } else {
         savedImage = await img.save(dp, fn, c.cookies, false, false);
       }

skills/baoyu-danger-gemini-web/scripts/package.json

@@ -3,6 +3,10 @@
   "private": true,
   "type": "module",
   "dependencies": {
-    "baoyu-chrome-cdp": "file:./vendor/baoyu-chrome-cdp"
+    "baoyu-chrome-cdp": "file:./vendor/baoyu-chrome-cdp",
+    "pngjs": "^7.0.0"
+  },
+  "devDependencies": {
+    "@types/pngjs": "^6.0.5"
   }
 }