(PECL imagick 2, PECL imagick 3)
Imagick::evaluateImage — Applies an expression to an image
$op, float $constant, int $channel = Imagick::CHANNEL_DEFAULT): boolApplys an arithmetic, relational, or logical expression to an image. Use these operators to lighten or darken an image, to increase or decrease contrast in an image, or to produce the "negative" of an image.
opThe evaluation operator
constantThe value of the operator
channelProvide 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.
Returns true on success.
Throws ImagickException on error.
Example #1 Using Imagick::evaluateImage()
Using evaluateImage to reduce opacity in an image.
<?php
// Create new object with the image
$im = new Imagick('example-alpha.png');
// Reduce the alpha by 50%
$im->evaluateImage(Imagick::EVALUATE_DIVIDE, 2, Imagick::CHANNEL_ALPHA);
// Output the image
header("Content-Type: image/png");
echo $im;
?>