Gemini Watermark

# Gemini Watermark Remover

Remove the visible Gemini AI watermark (star/sparkle logo) from generated images using mathematically accurate reverse alpha blending.

Fully offline — pure Python, no external binary downloads, no network access.

When to Use

• Remove the Gemini watermark from AI-generated images
• Batch process a directory of Gemini-generated images
• Clean images before publishing or sharing
• Automate watermark removal in pipelines

Quick Start

Install Dependencies (one-time)

```bash pip install Pillow numpy

# Recommended: use uv for faster, isolated installs uv pip install Pillow numpy ```

Requires: Python ≥ 3.9. No Rust toolchain, no compiled binaries, no downloads.

Basic Usage

```bash # Single image (auto-detect watermark, save as photo_cleaned.jpg) python3 scripts/remove_watermark.py photo.jpg

# Specify output path python3 scripts/remove_watermark.py photo.jpg -o clean_photo.jpg

# Batch process directory python3 scripts/remove_watermark.py ./input_dir -o ./output_dir

# Force removal without detection python3 scripts/remove_watermark.py photo.jpg -o clean.jpg --force ```

How It Works

Gemini adds a semi-transparent white star/sparkle logo to generated images using alpha blending:

``` watermarked = alpha * 255 + (1 - alpha) * original ```

This tool reverses the equation to recover the original pixels:

``` original = (watermarked - alpha * 255) / (1 - alpha) ```

The alpha map (watermark transparency pattern) is generated mathematically as a 4-pointed star (central Gaussian core + 4 elongated cardinal rays) at two sizes:

• 48×48 with 32 px margin — images where either dimension ≤ 1024 px
• 96×96 with 64 px margin — images where both dimensions > 1024 px

For improved accuracy you can supply your own alpha map derived from a background capture of the Gemini watermark on a white background (`--alpha-map`).

Detection

Before removal, a three-stage algorithm checks whether a watermark is present:

1. Spatial NCC (50% weight) — normalised cross-correlation with the alpha map
2. Gradient NCC (30% weight) — edge signature matching via Sobel operators
3. Variance Analysis (20% weight) — texture dampening detection

Images without detected watermarks are automatically skipped.

CLI Parameters

| Parameter | Short | Default | Description | |-----------|-------|---------|-------------| | `input` | | (required) | Input image file or directory | | `--output` | `-o` | `{name}_cleaned.{ext}` | Output file or directory | | `--force` | `-f` | `false` | Skip detection, process unconditionally | | `--threshold` | `-t` | `0.35` | Detection confidence threshold (0.0–1.0) | | `--force-small` | | `false` | Force 48×48 watermark size | | `--force-large` | | `false` | Force 96×96 watermark size | | `--alpha-map` | | (built-in) | Custom grayscale alpha map image | | `--verbose` | `-v` | `false` | Enable detailed output | | `--quiet` | `-q` | `false` | Suppress all non-error output |

Supported Formats

| Format | Read | Write | |--------|------|-------| | JPEG (.jpg, .jpeg) | Yes | Yes (quality 100) | | PNG (.png) | Yes | Yes | | WebP (.webp) | Yes | Yes | | BMP (.bmp) | Yes | Yes |

Usage Examples

```bash # Verbose output (shows detection confidence, watermark coordinates) python3 scripts/remove_watermark.py photo.png -o clean.png -v

# Lower detection threshold (more sensitive) python3 scripts/remove_watermark.py photo.jpg -t 0.15

# Force large watermark size regardless of image dimensions python3 scripts/remove_watermark.py photo.jpg --force-large -o clean.jpg

# Batch process, quiet mode python3 scripts/remove_watermark.py ./gemini_images/ -o ./cleaned/ -q

# Supply a custom alpha map for higher accuracy python3 scripts/remove_watermark.py photo.jpg --alpha-map my_alpha.png ```

Deriving a Custom Alpha Map

For pixel-perfect removal, capture the Gemini watermark on a pure white background and compute:

``` alpha(x, y) = max(R, G, B) / 255 ```

Save the result as a grayscale PNG and pass it via `--alpha-map`.

Output

• Single file — saves to `-o` path, or `{name}_cleaned.{ext}` by default
• Directory — saves all processed images to the output directory
• Skipped images — images without detected watermarks are not modified (unless `--force`)
• Exit code — 0 on success, 1 if any image fails

Troubleshooting

"No watermark detected" on a watermarked image

• Try lowering the threshold: `-t 0.1`
• Or bypass detection entirely: `--force`
• Consider supplying a custom alpha map for your watermark variant

Image looks distorted after removal

• The image may not have a Gemini watermark. Use detection (avoid `--force`)
• Try `--force-small` or `--force-large` to match the correct size
• Supply a custom alpha map for better precision

"Image too small" warning

The image dimensions are smaller than the watermark region. This typically means the image does not have a Gemini watermark.

ModuleNotFoundError: Pillow or numpy

```bash pip install Pillow numpy # or uv pip install Pillow numpy ```

Limitations

• Visible watermark only — this tool removes the visible star/sparkle logo watermark
• Cannot remove SynthID — Google's invisible watermark (SynthID) is embedded at the pixel level during generation and cannot be reversed
• Fixed position only — handles watermarks in the standard bottom-right position only
• Built-in alpha map is approximate — use `--alpha-map` with a captured reference for exact results