Signature Extractor

Extract handwritten signature ink from photographs or scanned documents, producing a clean transparent-background PNG. Removes white/light backgrounds, red stamps/seals, and colored paper textures while preserving black ink strokes.

When to Run

• User provides an image and asks to "remove background from signature", "make signature transparent", "extract signature", "remove stamp/印章"
• User asks to "darken signature ink", "make ink bolder", "填满笔迹", "加深签名"
• User asks to "upscale signature", "make signature clearer", "提高签名清晰度"
• User says "去掉底色", "去除背景", "签名透明", "提取签名", "去除印章"

Workflow

1. Identify the user's desired mode from their request:

| Request keywords | Mode | What it does |

|---|---|---|

| "填满", "加深", "实心", "加粗", "solid", default | solid | 3x upscale + sharpen + pure black opaque ink |

| "高清", "放大", "清晰", "upscale", "hd" | hd | 3x upscale + sharpen + smooth alpha gradient |

| "去掉底色", "提取", "简单去掉", "quick", "extract" | extract | Original size extraction with alpha gradient |

1. Run the extraction script:

```bash

python3 {baseDir}/scripts/extract_signature.py INPUT_IMAGE OUTPUT.png --mode MODE [--scale N]

```

• Default scale is 3 (for solid and hd modes). Adjust --scale if user specifies a different multiple.
• Output is always RGBA PNG format.

1. After completion, report: output dimensions, ink pixel count, and share the result with the user.

How It Works

The script isolates black ink using a three-channel color filter:

1. Brightness filter — pixels darker than a threshold are ink candidates
2. Red channel filter — R minus G must be less than 40, which excludes red stamps/seals
3. Saturation filter — low saturation ensures only true black/grey ink is captured, not colored marks

For solid and hd modes: LANCZOS upscaling → UnsharpMask sharpening → ink extraction → Alpha channel smoothing.

Prerequisites

pip install Pillow numpy