How does the tool know what's a stamp and what isn't?

It doesn't detect shapes — it keeps every pixel close to the ink color you specify (within a tolerance) and clears everything else. This works well when the stamp's ink is a distinct color from the surrounding document, like red or blue ink on white paper.

Can it extract a black-ink stamp from black text?

Not reliably. Because extraction is purely color-based, a black stamp mixed with black printed text will keep both, since the tool can't distinguish them by shape or context.

What does the tolerance setting do?

It controls how far a pixel's color can be from your chosen ink color (measured per RGB channel) and still count as a match; a higher tolerance keeps more shades, useful for scans with uneven ink saturation, but risks catching unrelated similarly-colored content.

What happens if nothing in the image matches the ink color?

The tool returns a clear error rather than a blank image, so you know to pick a different color or raise the tolerance instead of silently downloading an empty PNG.

Stamp Image Extractor - Isolate a Colored Stamp Mark from a Photo

Overview

Introduction

This tool pulls a colored stamp mark out of a photographed or scanned document by keeping only the pixels that match its ink color and making everything else transparent.

It's a real, working color-based extraction, not a full shape-recognition tool — that distinction is explained clearly below so you know exactly what it can and can't do.

What Is Stamp Image Extractor?

A pixel-level color-key extractor: for every pixel, it measures the maximum per-channel difference from your chosen ink hex color, keeps pixels within your tolerance, and zeroes the alpha channel of everything else.

It's the inverse selection of this category's chroma-key/background-removal tools, which discard the matched color instead of keeping it.

How Stamp Image Extractor Works

You upload an image and enter the hex color of the stamp's ink (e.g. #B22222 for a classic stamp red) along with a tolerance.

Every pixel within that tolerance of the target color keeps its original color and alpha; every other pixel becomes fully transparent, leaving just the stamp-colored regions visible.

When To Use Stamp Image Extractor

Use it when you've scanned or photographed a document with a distinctly colored stamp and want to isolate just that mark, for example to overlay it elsewhere or measure its position.

It works best when the stamp's ink color clearly differs from the surrounding text and background.

Often used alongside Image to Stamp Converter and Custom Stamp Design Creator.

Features

Advantages

Runs entirely client-side; your document image is never uploaded to a server.
Works for any ink color you specify, not just a single hardcoded shade.
Fails clearly with an explicit error when nothing matches, instead of silently returning a blank result.

Limitations

This is color-based extraction only — it cannot detect a stamp by its shape or position, so a stamp printed in the same color as surrounding text or images will not be isolated cleanly.
Uneven scan lighting or ink fading can require a higher tolerance, which in turn risks picking up unrelated similarly-colored content.

Examples

Extract a red approval stamp

Input

inkColorHex="#B22222", tolerance=40

Output

A transparent PNG showing only the red stamp mark, with the rest of the document cleared

A tolerance of 40 comfortably covers minor scan-induced color variation in the red ink.

No match found

Input

inkColorHex="#00FF00" on a document with no green ink

Output

An error: "No pixels matched the given ink color within tolerance"

The tool reports failure honestly instead of returning an all-transparent image.

Best Practices & Notes

Best Practices

Sample the stamp's actual ink color with a color picker before entering the hex value for the best match.
Start with a moderate tolerance (30-50) and raise it gradually if the extraction misses lighter parts of the ink.

Developer Notes

The lib function is a genuinely new pixel-selection routine (keep-if-matching, versus the existing remove-if-matching chroma-key tools in this category), implemented as a pure function over a PixelBuffer with no DOM dependency so it's fully unit-testable; full shape-based stamp detection is out of scope and documented here rather than faked.

Stamp Image Extractor Use Cases

Isolating a colored approval or notary stamp from a scanned form
Pulling a company stamp mark out of a signed document photo
Preparing a stamp graphic for reuse after removing its paper background

Common Mistakes

Trying to extract a black-ink stamp from a document with lots of black text — color-only matching can't tell them apart.
Using too low a tolerance on a poorly scanned image, which misses faded parts of the ink and leaves gaps in the extracted mark.

Tips

If extraction misses part of the stamp, nudge the tolerance up a little rather than jumping straight to a much higher value.
Combine this with the PNG Cropper tool afterward to trim the transparent margin around the extracted mark.

Stamp Image Extractor