Removing Gemini AI Watermarks: A Deep Dive into Reverse Alpha Blending

An open-source tool to cleanly remove those pesky watermarks from your AI-generated images.

I recently discovered an open-source Gemini watermark remover that delivers excellent results. While the original author, Allen Kuo, created a Windows command-line program, the community has since developed web versions and Tampermonkey scripts based on his work.

I personally tested these tools and found them to be incredibly fast and effective. The Tampermonkey script, in particular, is a game-changer—it automatically removes watermarks directly on the Gemini webpage.

Project Links:

• GitHub (Original Windows Tool):https://github.com/allenk/GeminiWatermarkTool
• GitHub :https://github.com/journey-ad/gemini-watermark-remover
• Web Version:https://banana.ovo.re

The underlying logic of this tool is quite interesting, relying on a reverse alpha blending algorithm. The author provided a series of mathematical formulas that, while complex to the uninitiated, produce results that are shockingly precise.

The Problem: Beautiful Images, Annoying Watermarks

If you’ve been using Google’s Gemini AI for image generation—whether it’s Gemini Nano, Gemini Flash, or Gemini Pro—you’ve probably noticed that every generated image comes with a semi-transparent watermark in the bottom-right corner.

While transparency about AI-generated content is important, there are legitimate scenarios where these watermarks become a headache:

• Presentations: Preparing slides for a business meeting where the watermark is distracting.
• Design mockups: The watermark clashes with carefully crafted layouts.
• Personal creative projects: Needing a clean image for mood boards or concept art.
• Social media content: The watermark distracts from the visual story.

Introducing Gemini Watermark Tool

The Gemini Watermark Tool is a lightweight, standalone utility designed to remove these watermarks accurately and efficiently.

Key Features

• One-click removal: Drag and drop an image onto the executable (Windows version).
• Batch processing: Process hundreds of images in seconds.
• Mathematically accurate: Uses reverse alpha blending, not crude inpainting.
• Zero dependencies: Single .exe file, no installation required.
• Open source: MIT licensed, free to use and modify.

How to Use (Windows Version)

The Simplest Way: Drag & Drop

1. Download GeminiWatermarkTool.exe from the GitHub releases page.
2. Drag your watermarked image onto the executable.
3. The watermark is removed in-place.

Command Line Usage

For more control:

# Remove watermark, save to new file
GeminiWatermarkTool.exe -i watermarked.jpg -o clean.jpg

# Process an entire folder
GeminiWatermarkTool.exe -i ./input_folder/ -o ./output_folder/

# Force specific watermark size (if auto-detection fails)
GeminiWatermarkTool.exe -i image.jpg -o output.jpg --force-small

Watermark Size Detection

Gemini uses different watermark sizes based on image dimensions:

The tool automatically detects which size to use, but you can override it with --force-small or --force-large.

The Technical Magic: Reverse Alpha Blending

This is where it gets interesting. Most people assume watermarks are simply “stamped” onto images. But Gemini uses something more sophisticated: alpha blending.

The formula is:

watermarked = α × logo + (1 - α) × original

Where:

• watermarked is the final pixel value you see.
• original is the original pixel value (what we want to recover).
• α (alpha) is the transparency factor (0 = fully transparent, 1 = fully opaque).

This creates that semi-transparent overlay effect.

Reversing the Process

By statistically analyzing and comparing values, we can reconstruct the Alpha map. Once α is known for every pixel, we can algebraically reverse the blending formula:

original = (watermarked - α × 255) / (1 - α)

For each pixel in the watermarked region:

1. Get the alpha value from the pre-computed alpha map.
2. Apply the reverse formula.
3. Clamp the result to the valid range [0, 255].

The result is a mathematically accurate reconstruction of the original pixel values.

Why This Works Better Than Alternatives

• Inpainting: Guesses what pixels should be, often creating artifacts.
• Clone stamping: Manual and inconsistent.
• Content-aware fill: Can produce blurry results.

This approach doesn’t guess. It calculates the exact original values using the known watermark pattern. The only error comes from minor 8-bit quantization, which is imperceptible.

For Developers

The tool is open source under the MIT License.

• Source Code:github.com/allenk/GeminiWatermarkTool

Building from Source

# Clone the repository
git clone https://github.com/allenk/GeminiWatermarkTool.git
cd GeminiWatermarkTool

# Configure with vcpkg
cmake -B build -S . \
  -DCMAKE_TOOLCHAIN_FILE=[vcpkg-root]/scripts/buildsystems/vcpkg.cmake \
  -DVCPKG_TARGET_TRIPLET=x64-windows-static \
  -DSTANDALONE_MODE=ON

# Build
cmake --build build --config Release

Disclaimer

This tool is provided for personal and educational use. Always backup your original images before processing. Respect content policies and legal implications.