Modify Php function to crop image border by X pixels

I have this PHP function that I use on Behat automation which takes a screenshot of an element of the page, cropping the image:

protected function takeElementScreenshot($filename, $folder, $selector)
{
$element = $this->findElement($selector);
$driver = $this->getSession()->getDriver();
$this->iScrollToTheElement('top', $selector);
$previousWindowHeight = $driver->evaluateScript("window.outerHeight");
$previousViewportHeight = $driver->evaluateScript("window.innerHeight");
$domElement = "document.evaluate("$selector", document, null," .
"XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue";
$elementRect = $driver->evaluateScript("$domElement.getBoundingClientRect()");
if ($previousViewportHeight < $elementRect["height"]) {
$windowWidth = $driver->evaluateScript("window.outerWidth");
$offset = $previousWindowHeight - $previousViewportHeight;
$this->iSetBrowserWindowSizeToX($windowWidth, $elementRect["height"] + $offset);
}
$elementRect = $driver->evaluateScript("$domElement.getBoundingClientRect()");
$x = $elementRect["left"];
$y = $elementRect["top"];
$elementWidth = $elementRect["width"];
$elementHeight = $elementRect["height"];
$this->saveScreenshot($filename, $folder);
$screenshot = new Imagick("$folder/$filename");
$imageWidth = $screenshot->getimagewidth();
$imageHeight = $screenshot->getimageheight();
$cropWidth = min($imageWidth - $x, $elementWidth);
$cropHeight = min($imageHeight - $y, $elementHeight);
$screenshot->cropimage($cropWidth, $cropHeight, $x, $y);
$screenshot->writeImage("$folder/$filename");

if ($windowWidth) {
$this->iSetBrowserWindowSizeToX($windowWidth, $previousWindowHeight);
}
}


The problem is that when it crops, sometimes it does not crop perfectly. I would take a long time to explain what happens so I will go direct to the question: Is there a way to remove X pixels from the borders after if crops?

Example: if it takes a screenshot of an element and the result image is 500x500, I would like it to crop 2 pixels from the borders, resulting in an image of 498x498 pixels. The pixel amount I'm not sure yet how much it will be enough, so I will test it until I find a good value.

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