Question

What is a fast way to tell what dimensions an Imagick instance will become when you call Imagick::thumbnailImage($w, $h) on it?

Answer 1

I could not find an algorithm for finding the dimensions that Imagick::thumbnailImage($w, $h) gives that handles all possible situations with 100% accuracy. (e.g. cases where $w or $h are 0, etc.) So, I made this function:

function thumbSize($pic, $thumbW, $thumbH) {
    //make a white image of the same size
    $picsize = $pic->getImageGeometry();
    $whitepic=new Imagick();
    $whitepic->newImage($picsize['width'], $picsize['height'], "white");
    $whitepic->thumbnailImage($thumbW, $thumbH);
    return $whitepic->getImageGeometry();
}

Sadly, it has to resize an image to work; it is many times slower than an algorithm-based solution. But it works.

If anyone else has a better answer, I’ll check it instead.