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 keywordsModeWhat it does"填满", "加深", "实心", "加粗", "solid", defaultsolid3x upscale + sharpen + pure black opaque ink"高清", "放大", "清晰", "upscale", "hd"hd3x upscale + sharpen + smooth alpha gradient"去掉底色", "提取", "简单去掉", "quick", "extract"extractOriginal size extraction with alpha gradient

2. 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.

3. 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#

bash

pip install Pillow numpy