Negates the colors in the reference image. The Grayscale option means that only grayscale values within the image are negated.
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Image
Pixels
Channel
Negates the colors in the reference image. The Grayscale option means that only grayscale values within the image are negated.
Parameters
grayboolWhether to only negate grayscale pixels within the image.
channelintProvide any channel constant that is valid for your channel mode. To apply to more than one channel, combine channeltype constants using bitwise operators. Refer to this list of channel constants.
function negateImage($imagePath, $grayOnly, $channel)
{
    $imagick = new \Imagick(realpath($imagePath));
    $imagick->negateImage($grayOnly, $channel);
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}