Edge Detection (Canny)
Detect the edges in a photo using OpenCV's Canny edge detector, all in your browser. Tune the sensitivity with two thresholds, flip to dark lines on white for a clean line-art look, and download the result. OpenCV loads on demand and your image is processed locally, never uploaded.
How to detect edges in an image
- Drop an image in, or click to browse.
- Adjust the low and high thresholds, or pick a preset.
- Download the edge map as a PNG.
Examples
Outline a photo
A portrait photo, Balanced preset
A black image with white edges tracing the main shapes
Frequently asked questions
Is my image uploaded anywhere?
No. Edge detection runs entirely in your browser with OpenCV compiled to WebAssembly. The image never leaves your device.
What do the two thresholds do?
Canny uses a low and a high threshold. Edges above the high threshold are always kept; weaker edges are kept only if they connect to a strong edge. Lower thresholds find more edges (and more noise); higher thresholds keep only the strongest.
Why is the first run slow?
The OpenCV engine downloads once on first use, then is cached. Larger images also take a moment to process.
Can I get black lines on a white background?
Yes. Turn on invert for dark edges on white, which is ideal for a clean line-art or coloring-page style.
Related tools
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Turn any photo into a printable black-and-white coloring page with edge detection. Adjust the line detail, then download a PNG. Free and runs in your browser.
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APNG Detector
Check whether a PNG file is an animated PNG (APNG) in your browser. See the frame count, loop count, and dimensions read straight from the file. Private.