How do I know what coordinates to enter?

The preview after upload shows the signature's full pixel dimensions; use those to estimate the top-left x/y corner and the width/height of the region you want to keep.

What happens if my crop rectangle goes outside the image?

The tool rejects it with an error rather than silently clamping it, so you always know exactly what region was cropped.

Does cropping remove the background?

No, cropping only cuts a rectangular region out of the existing pixels; it doesn't change any pixel's color or transparency. Use a background remover tool separately if needed.

Can I crop to a non-rectangular shape?

No, this tool only supports rectangular crops. For trimming exactly to the signature's visible content regardless of shape, use an edges/padding-trimming tool instead.

Signature Cropper - Crop a Signature PNG Online

Overview

Introduction

This tool crops a rectangular region out of a signature PNG entirely in your browser, given exact pixel coordinates.

It's a precise, predictable way to trim stray marks or isolate just the part of a scan you actually want.

What Is Signature Cropper?

A client-side rectangular crop tool that reads the source signature's pixel data and copies out the sub-rectangle you specify.

It requires the crop rectangle to lie entirely within the source image's bounds.

How Signature Cropper Works

Given a top-left corner (x, y) and a width/height, the tool creates a new, smaller pixel buffer and copies each pixel from the corresponding position in the source image.

All four values must be whole numbers, and the rectangle must not extend past the source image's edges.

When To Use Signature Cropper

Use it to trim excess whitespace, stray pen marks, or scanner artifacts from around a signature.

It's also useful for isolating one signature out of a scan that captured multiple signatures on the same page.

Often used alongside Signature Resizer and Signature Image Extractor.

Features

Advantages

Precise, coordinate-based control over exactly what's kept.
Rejects out-of-bounds crops with a clear error instead of silently clamping them.
Runs entirely client-side.

Limitations

Only supports rectangular crops; there's no automatic content-aware detection of where the signature actually is.
Requires knowing (or estimating) exact pixel coordinates, which can take some trial and error.

Examples

Trim a stray mark

Input

A 400x150 signature scan with a smudge in the corner, cropped to (10, 10, 350, 120)

Output

A 350x120 PNG with the smudge cut out

Choosing a rectangle that excludes the smudged corner removes it entirely.

Isolate one of two signatures

Input

A scan with two signatures side by side, cropped to just the left half

Output

A PNG containing only the first signature

A rectangular crop that spans just one signature's region separates it from the rest of the page.

Best Practices & Notes

Best Practices

Check the source image's dimensions first (via the dimensions finder tool) before entering crop coordinates.
If you just need to trim empty transparent margin automatically, use the signature image extractor instead of manual coordinates.

Developer Notes

This tool is a thin wrapper around the shared cropPng function; the rectangular-crop math is identical regardless of whether the subject is a signature or any other PNG.

Signature Cropper Use Cases

Removing a stray mark or smudge from a signature scan
Separating multiple signatures captured on one page
Trimming a signature down to a specific aspect ratio before use elsewhere

Common Mistakes

Entering a width/height that extends past the image's edge, which the tool rejects rather than silently clamping.
Forgetting that coordinates are pixels from the top-left corner, not percentages.

Tips

Use the dimensions finder tool first to confirm the source image's exact pixel size.
For automatic trimming to the visible signature content, prefer the signature image extractor over manual cropping.

Signature Cropper