Remove background after comparing two images with Imagick - php

Question

i'm new using imagick with php and i have a problem:
I'm comparing two images with the compareImages() function. I'm using the same code as in the documentation page:
<?php
$image1 = new imagick("image1.png");
$image2 = new imagick("image2.png");
$result = $image1->compareImages($image2, Imagick::METRIC_MEANSQUAREERROR);
$result[0]->setImageFormat("png");
header("Content-Type: image/png");
echo $result[0];
?>
This code is working right, but the result image has a background with the original image with a bit of opacity.
I've been searching and I found the result that I want but with imagemagick commands:
http://www.imagemagick.org/Usage/compare/
My current result is like the image of the first command ("compare bag_frame1.gif bag_frame2.gif compare.gif") and I want a result like the shown in this command:
compare bag_frame1.gif bag_frame2.gif \
-compose Src compare_src.gif
Is there any way of doing this with the compareImages() function of imagick?
Thanks

Answer 1

You'll need to use Imagick::SetOption before reading the first image.
<?php
$image1 = new imagick(); // Init empty object
$image2 = new imagick("image2.png");
// Set Lowlight (resulting background) to transparent, not "original image with a bit of opacity"
$image1->setOption('lowlight-color','transparent');
// Switch the default compose operator to Src, like in example
$image1->setOption('compose', 'Src');
// Now read image
$image1->readImage("image1.png");
// Result will not have a background
$result = $image1->compareImages($image2, Imagick::METRIC_MEANSQUAREERROR);