/**
* By doing random sampling from the image, find the most energetic point on the passed in
* image
*
* @param Imagick $image
* @return array
*/
protected static function getHighestEnergyPoint(Imagick $image)
{
// It's more performant doing random pixel uplook via GD
if (($im = imagecreatefromstring($image->getImageBlob())) === false) {
throw new Exception('GD failed to create image from string');
}
$size = $image->getImageGeometry();
$xcenter = 0;
$ycenter = 0;
$sum = 0;
// Only sample 1/50 of all the pixels in the image
$sampleSize = round($size['height'] * $size['width']) / 50;
for ($k = 0; $k < $sampleSize; $k++) {
$i = mt_rand(0, $size['width'] - 1);
$j = mt_rand(0, $size['height'] - 1);
$rgb = imagecolorat($im, $i, $j);
$r = $rgb >> 16 & 0xff;
$g = $rgb >> 8 & 0xff;
$b = $rgb & 0xff;
$val = Color::rgb2bw($r, $g, $b);
$sum += $val;
$xcenter += ($i + 1) * $val;
$ycenter += ($j + 1) * $val;
}
if ($sum) {
$xcenter /= $sum;
$ycenter /= $sum;
}
$sum = $sum / round($size['height'] * $size['width']);
return array('x' => $xcenter, 'y' => $ycenter, 'sum' => $sum);
}
/**
* Find out the entropy for a color image
*
* If the source image is in color we need to transform RGB into a grayscale image
* so we can calculate the entropy more performant.
*
* @param Imagick $image
* @return float
*/
protected static function colorEntropy(Imagick $image)
{
$histogram = $image->getImageHistogram();
$newHistogram = array();
// Translates a color histogram into a bw histogram
$colors = count($histogram);
for ($idx = 0; $idx < $colors; $idx++) {
$colors = $histogram[$idx]->getColor();
$grey = Color::rgb2bw($colors['r'], $colors['g'], $colors['b']);
if (isset($newHistogram[$grey])) {
$newHistogram[$grey] += $histogram[$idx]->getColorCount();
} else {
$newHistogram[$grey] = $histogram[$idx]->getColorCount();
}
}
return static::getEntropy($newHistogram, static::area($image));
}
