True Sobel gradient detection
The filter measures brightness change in both directions and keeps the magnitude, so it draws real structural edges rather than a naive high-contrast outline.
ImageRuns in your browser
Edge Detect Image
Trace the outlines of any photo into clean black-and-white line art.
- Upload
- Single file · 25 MB max
- Privacy
- Nothing is uploaded
- Cost
- Free · no sign-up · no watermark
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Processed entirely on your device
Your file is read, transformed and re-encoded inside this browser tab using JavaScript. There is no upload endpoint — nothing leaves your machine, nothing is stored, and the result is created as a local object URL that disappears when you close the page.
Overview
About the Edge Detect Image
Detect edges in an image with a Sobel filter that turns any photo into crisp outlines on a white field. Runs on your device — nothing is uploaded.
How Sobel edge detection works
The Sobel operator looks at a 3×3 window around every pixel and estimates how quickly brightness changes horizontally and vertically. Where the image is flat, both gradients are near zero and the output stays white. Where there is a strong boundary, the combined gradient magnitude is high and a dark line appears.
What it is good for
Edge maps are the starting point for many workflows: tracing a photo into vector paths, preparing artwork for engraving or cutting, creating technical-looking diagrams, or producing a colouring-page outline from a picture. Because the output is clean black on white, it is easy to threshold or vectorise further.
Getting the best lines
Edges follow contrast, so images with clear separation between subject and background trace best. Soft, low-contrast photos give faint results; running a contrast or sharpen pass first strengthens the boundaries before you detect them.
Runs entirely on your device
The gradient convolution happens on an in-browser canvas at full resolution and is exported as a lossless PNG, keeping your source private and the lines crisp.
Step by step
How to use the Edge Detect Image
Drop an image with defined shapes onto the upload area.
The Sobel edge map renders instantly as outlines on white.
High-contrast subjects give the cleanest lines.
Download the edge-detected PNG, ideal as a tracing or vector base.
Why use it
Benefits and common use cases
What this tool is good for, and what it deliberately does not try to do.
Perfect pre-step for tracing
Clean line art is exactly what you want before vectorising, engraving, laser-cutting or turning a photo into a colouring-page style drawing.
Instant, local, private
The gradient pass runs on an in-browser canvas and exports PNG, so even sensitive images are processed without any upload.
Questions
Frequently asked questions
Short, honest answers about quality, limits and privacy.
Why are some edges missing?
Sobel only draws where brightness changes sharply. Low-contrast boundaries and smooth gradients produce faint or no lines. Boost contrast first to strengthen them.
Is this the same as a pencil-sketch filter?
It is the core step of one. Edge detection gives the raw outlines; a sketch look usually adds tone and texture on top of these same edges.
Can I get coloured edges?
This tool outputs a grayscale edge map, which is the standard, most useful result for tracing and line art.