Remove Watermark

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name: remove-watermark description: Remove light-colored text watermarks from white-background document images (exam papers, scanned documents). No API key needed - pure local image processing. Use when the user wants to remove watermarks, clean up document screenshots, or remove light text overlays from images.

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Remove Watermark

Remove watermarks from white-background document images. Pure local processing, no API key needed.

When to Use

Trigger this skill when the user wants to:

Remove watermarks from document images or screenshots

Clean up exam paper screenshots for printing

Remove light text overlays (e.g., "公众号·xxx", website names)

Workflow: 4-Step Process

The script path is scripts/remove_watermark.py relative to this SKILL.md. Use uv run --with Pillow --with numpy (add --with scipy only when using --region full).

Step 1: Visual Analysis (Claude reads the image)

Use the Read tool to look at a sample image. Identify:

Is there a watermark? If no, skip processing.

Where is it? (bottom-right corner, center, scattered across the image)

What type? (light gray text, dark logo/stamp, colored)

Does it overlap with content text?

Estimate the watermark region as approximate percentages: y0%, y1%, x0%, x1%.

Step 2: Brightness Analysis (script analyzes the region)

Run the analyze subcommand on the watermark region to determine the right threshold:

uv run --with Pillow --with numpy python3 /scripts/remove_watermark.py analyze  --region "y0,y1,x0,x1"

Example: analyze sample.jpg --region "94,100,60,100"

This prints brightness distribution and a suggested threshold.

Step 3: Remove Watermark

Use the suggested threshold and region from Steps 1-2:

# Region mode (preferred - zero damage to text outside the region)
uv run --with Pillow --with numpy python3 /scripts/remove_watermark.py remove  -o 
 --region "y0,y1,x0,x1" --threshold 
Full mode (when watermark is scattered everywhere - needs scipy)
uv run --with Pillow --with numpy --with scipy python3 /scripts/remove_watermark.py remove  -o 
 --threshold 

Region presets: bottom-right, bottom-left, top-right, top-left, bottom, top, right, left, center, full

Custom region: --region "y0,y1,x0,x1" as percentages (e.g., "94,100,60,100" = bottom 6%, right 40%)

Step 4: Verify and Auto-Retry

Use the Read tool to check the output image. You MUST verify and retry if needed — do not stop after one attempt.

Check these two things: 1. Is the watermark gone? 2. Is the text content intact (not lightened or damaged)?

If watermark is still visible, retry with adjusted parameters:

| Problem | Fix | |---------|-----| | Watermark still visible | Lower the threshold (e.g., 180 → 130 → 80) | | Only partially removed | Expand the region (e.g., widen by 5-10% in each direction) | | Text got damaged/lightened | Raise the threshold or shrink the region to avoid text areas | | Wrong area processed | Re-examine the image and correct the region coordinates |

Retry rules:

Retry up to 3 times with different parameters before giving up

Each retry: adjust ONE parameter at a time (threshold OR region, not both)

If the suggested threshold from analyze didn't work, try halving it

If threshold=50 still doesn't remove the watermark, try threshold=1 with a tighter region (the region likely has no real content, so blanking it entirely is safe)

After 3 failed attempts, report to the user what was tried and ask for guidance

Command Reference

analyze

remove_watermark.py analyze  [--region REGION]

Prints brightness distribution and suggested threshold for a region.

remove

remove_watermark.py remove  [-o OUTPUT] [--region REGION] [--threshold N] [--enhance]

| Flag | Default | Description | |------|---------|-------------| | --region | full | Region to process (preset name or y0,y1,x0,x1) | | --threshold | 180 | Brightness cutoff for watermark pixels | | --enhance | off | Boost text contrast after removal | | --preview | off | Print stats without saving |

Tips

Region mode is always preferred over full mode when watermark is localized. It leaves all text perfectly intact.

For dark watermarks (logo, stamps), use a low threshold (80-120) with a tight region.

For light gray text watermarks, use a higher threshold (160-200).

Same batch: if all images in a folder have the same watermark position, analyze one image and apply the same settings to all.

Combine with image-to-pdf skill: remove watermarks first, then combine into PDF.

Region mode is always preferred over full mode when watermark is localized. It leaves all text perfectly intact.

For dark watermarks (logo, stamps), use a low threshold (80-120) with a tight region.

For light gray text watermarks, use a higher threshold (160-200).

Same batch: if all images in a folder have the same watermark position, analyze one image and apply the same settings to all.

Combine with image-to-pdf skill: remove watermarks first, then combine into PDF.