PHP/ImageMagic Get the “shadow” of an image

Question

I would like to script PHP/ImageMagic in order to produce the \"shadow\" of a given image. Like in this example (done manually in GFXeditor) :

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Answer 1

Use convert with -threshold option?

EDIT: oops... from PHP? Imagick::thresholdImage?

I wonder if it isn't more like a mask than a shadow? In the context of IM, shadow looks like a blurry copy of the image.

Answer 2

Try the edge detection chapter in the ImageMagick examples.