使用Image Magick获取图像形状边缘

Question

I am new to ImageMagick and Imagick library in php, and I want to know how can I make everything transparent but leave only the edges of the shape in a png image.

For example I have this picture:

And I want to keep only a thin line formed by the edges of the eagle, and fill the inside of the eagle with transparent color.

Or as an alternative how can I change the black eagle color into a brown rgba color with opacity 0.4 using Image Magick library with php and GD library?

Answer 1

Something like this to detect edges:

convert eagle.png --edge 3 eagle-edges.png

Within PHP you can use bool Imagick::edgeImage(float $radius).