The edge-detection filter eliminates detail in an image and only displays object outlines.
The filter works by reading the values of surrounding pixels.
This means that an edge-detect followed by image-resize will be different to image-resize followed by edge-detect.
The precise effect obtained also depends on the value set in the 'Threshold Level' box
This can vary from 0 (black) to 255 (white).
Initially, it is set to '16' but may be altered to suit a particular image.
As soon as you click 'OK' the conversion process begins and a progress-bar is displayed at bottom-left of the window.
To return to the unfiltered image, click 'Undo' .
In the normal (not 'Easy Adjustment') viewing modes, the Edge filter may be used for a purely pictorial effect to reduce a scene to its outlines.
After saving the scene, you may 'Undo' to return to the original image.
Reducing an image to its edge outlines can also greatly simplify image-correction, particularly when using the 'Easy Adjustment' option.
In that case, the Easy Adjustment values are applied to the original images.
Note that in the processed image, the edges in the left view are cyan.
When viewed through the red lens, the red outlines of the right view disappear into the 'white' background and the cyan outlines in the left view appear black.