Extract all edge lines from photos, like using a pen to outline a photo, drawing out the contours and detail boundaries of objects.

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Working Principle

Imagine you are an artist who needs to use a pen to outline a photo. The Canny node acts like an intelligent assistant, helping you decide where to draw lines (edges) and where not to.

This process is like a screening job:

  • High threshold is the “must draw line standard”: only very obvious and clear contour lines will be drawn, such as facial contours of people and building frames
  • Low threshold is the “definitely don’t draw line standard”: edges that are too weak will be ignored to avoid drawing noise and meaningless lines
  • Middle area: edges between the two standards will be drawn together if they connect to “must draw lines”, but won’t be drawn if they are isolated

The final output is a black and white image, where white parts are detected edge lines and black parts are areas without edges.

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Inputs

Parameter NameData TypeInput TypeDefaultRangeFunction Description
imageIMAGEInput--Original photo that needs edge extraction
low_thresholdFLOATWidget0.40.01-0.99Low threshold, determines how weak edges to ignore. Lower values preserve more details but may produce noise
high_thresholdFLOATWidget0.80.01-0.99High threshold, determines how strong edges to preserve. Higher values only keep the most obvious contour lines

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Outputs

Output NameData TypeDescription
imageIMAGEBlack and white edge image, white lines are detected edges, black areas are parts without edges

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Parameter Comparison

Common Issues:

  • Broken edges: Try lowering high threshold
  • Too much noise: Raise low threshold
  • Missing important details: Lower low threshold
  • Edges too rough: Check input image quality and resolution