Detect the edges in a photograph. A named 3×3 Sobel operator, a threshold and a scale—an inspectable gradient map, not an unexplained sketch filter.
This is a rebuild: your photo is taken apart and remade, not just recoloured. It runs in this tab and nothing is uploaded.
Tip Clean shapes against an even ground produce a readable map; noise and foliage produce many truthful but distracting edges.
The operation behind the appearance
Red, green and blue are first reduced to weighted luminance. Two 3×3 Sobel kernels measure change across x and y; their Euclidean magnitude is multiplied by strength and compared with the threshold. Inversion changes presentation only, turning bright-on-black into black-on-white.
The controls are measurements
- Threshold
- The minimum gradient magnitude allowed to remain.
- Gradient strength
- A multiplier on all measured edge magnitudes.
- Black lines on white
- An inversion after measurement, not a different detector.
Where the construction breaks
Sobel locates contrast, not meaning. Noise, compression blocks, skin texture and patterned fabric can be stronger than the outline a person wanted. Blur the source beforehand when the job is structural edges; keep the unblurred source when fine texture is the subject.
The preview, draft and export all run the same kernel. Parameters measured in pixels are scaled with the source, so a chosen tile, band or radius does not become unexpectedly finer in the downloaded file.
Questions about this effect
What counts as an edge?
A rapid change in Rec. 709 luminance across neighbouring pixels. The Sobel pair measures horizontal and vertical change and combines their magnitudes.
Why does texture fill with lines?
Texture is made of local brightness changes too. The operator knows nothing about objects, so a leaf vein and a face outline are both gradients.
What does threshold remove?
Gradient magnitudes below the chosen value are written as zero before inversion. Raising it suppresses weak texture and also discards faint real boundaries.
Related on this site
- Blur stylesSoft, horizontal and vertical averaging with a stated radius.
- PosteriseContinuous tone reduced to measured channel levels, with optional pre-dither.
- HalftoneDots on a rotated screen, one plate or four, with the angles a press would use.
- Filter picture online41 colour looks and 20 effects, chosen from your own photograph rather than from a list of names.
Rendered on your computer, not on a server.