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) .

Answer 2

I managed to get the result with these commands though I haven't tested yet on other images, only on the one with the eagle.

exec('convert eagle.png -charcoal 1 neweagle.png');
exec('convert neweagle.png -transparent white neweagle.png'); 

I am open to other better solutions!!

Also would be great if some knows how to do these commands from the php library without the exec.

Answer 3

Option 1

If you want the outline of the eagle black and everything else transparent, you can use this:

convert eagle.png -channel RGBA -separate -delete 0-2 -edge 1 -threshold 1 -transparent black +channel -negate result.png

That separates the image into RGBA channels and discards all except the alpha channel. It then finds the edges of the alpha channel (which show up as white on black) and then makes black pixels transparent and inverts the white ones to black.

My PHP implementation is as follows:

<?php
// convert eagle.png -channel RGBA -separate -delete 0-2 -edge 1 -threshold 1 -transparent black +channel -negate result.png
   $image=new Imagick('eagle.png');
   $image->separateimagechannel(Imagick::CHANNEL_OPACITY);
   $image->edgeImage(1);
   $image->thresholdImage(1);
   $image->transparentPaintImage("black",0.0,10,false);
   $image->negateImage(false);
   $image->writeimage('result.png');
?>

Option 2

If you want to make the black body of the eagle into 40% opaque dark brown, you can do this:

convert eagle.png -channel RGBA -fill "rgba(101,67,33,0.4)" -fuzz 10% -opaque black result.png

My PHP implementation is as follows:

<?php
// convert eagle.png -channel RGBA -fill "rgba(101,67,33,0.5)" -fuzz 10% -opaque black answer2.png
   $image=new Imagick('eagle.png');
   $image->opaquePaintImage("black","rgba(101,67,33,0.4)",10,false,imagick::CHANNEL_ALL);
   $image->writeimage('result2.png');
?>