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<?php |
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namespace Stojg\Crop; |
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use Imagick; |
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use ImagickPixel; |
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use InvalidArgumentException; |
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/** |
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* Class CropEntropy |
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* |
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* This class will help on finding the most energetic part of an image. |
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* |
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* @package Stojg\Crop |
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*/ |
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class CropEntropy |
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{ |
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/** |
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* @var Imagick |
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*/ |
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protected $image = null; |
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/** |
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* CropEntropy constructor |
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* |
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* @param Imagick|null $image |
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*/ |
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public function __construct(Imagick $image = null) |
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{ |
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if ($image !== null) { |
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$this->image = $image; |
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} else { |
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$this->image = new Imagick(); |
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} |
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} |
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/** |
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* @return Imagick |
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*/ |
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public function getImage() |
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{ |
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return $this->image; |
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} |
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/** |
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* @param int $width - The width of the region to be extracted |
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* @param int $height - The height of the region to be extracted |
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* @param int $x - X-coordinate of the top-left corner of the region to be extracted |
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* @param int $y -Y-coordinate of the top-left corner of the region to be extracted |
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* @return CropEntropy |
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*/ |
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public function getRegion($width, $height, $x, $y) |
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{ |
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return new CropEntropy($this->image->getImageRegion($width, $height, $x, $y)); |
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} |
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/** |
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* Get the area in pixels for this image |
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* |
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* @return int |
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*/ |
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public function area() |
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{ |
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$size = $this->image->getImageGeometry(); |
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return $size['height'] * $size['width']; |
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} |
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/** |
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* @param CropEntropy $b |
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* @return int |
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*/ |
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public function compare(CropEntropy $b) |
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{ |
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$aValue = $this->getGrayScaleEntropy(); |
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$bValue = $b->getGrayScaleEntropy(); |
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if ($aValue == $bValue) { |
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return 0; |
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} |
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return ($aValue < $bValue) ? -1 : 1; |
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} |
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/** |
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* Calculate the entropy for this image. |
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* |
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* A higher value of entropy means more noise / liveliness / color / business |
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* |
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* @return float |
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* |
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* @see http://brainacle.com/calculating-image-entropy-with-python-how-and-why.html |
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* @see http://www.mathworks.com/help/toolbox/images/ref/entropy.html |
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*/ |
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public function getGrayScaleEntropy() |
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{ |
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$histogram = $this->image->getImageHistogram(); |
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return $this->getEntropy($histogram, $this->area()); |
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} |
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/** |
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* |
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* @param string $axis - must be either 'x' or 'y' |
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* @param int $sliceSize |
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* @return int |
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*/ |
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public function getMidPoint($axis, $sliceSize = 20) |
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{ |
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if (!in_array($axis, ['x', 'y'])) { |
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throw new InvalidArgumentException('argument $axis must be either "x" or "y"'); |
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} |
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$targetSize = $sliceSize; |
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$clone = clone($this->image); |
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$clone->modulateImage(100, 0, 100); |
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$clone->setImageColorspace(Imagick::COLORSPACE_GRAY); |
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$image = new CropEntropy($clone); |
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$size = $clone->getImageGeometry(); |
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$min = 0; |
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if ($axis === 'x') { |
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$max = $size['width']; |
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} else { |
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$max = $size['height']; |
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} |
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$a = null; |
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$b = null; |
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// until we have a slice that would fit inside the target size |
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do { |
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// Make sure that we don't try to slice outside the image |
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$sliceSize = min($max - $min - $targetSize, $sliceSize); |
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if ($a === null) { |
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if ($axis === 'x') { |
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$a = $image->getVerticalSlice($min - 1, $sliceSize); |
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} else { |
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$a = $image->getHorizontalSlice($min - 1, $sliceSize); |
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} |
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} |
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if ($b === null) { |
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if ($axis === 'x') { |
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$b = $image->getVerticalSlice($max - $sliceSize - 1, $sliceSize); |
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} else { |
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$b = $image->getHorizontalSlice($max - $sliceSize - 1, $sliceSize); |
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} |
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} |
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// a has higher energy, so create a new b slice, i.e move b $sliceSize against a |
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if ($a->compare($b) > 0) { |
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$max -= $sliceSize; |
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$b = null; |
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} else { |
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$min += $sliceSize; |
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$a = null; |
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} |
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} while ($max - $min > $targetSize); |
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return $min + ($sliceSize / 2); |
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} |
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/** |
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* |
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* @param ImagickPixel[] $histogram |
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* @param int $area |
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* @return float |
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*/ |
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protected function getEntropy($histogram, $area) |
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{ |
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$value = 0.0; |
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foreach ($histogram as $pixel) { |
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// calculates the percentage of pixels having this color value |
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$p = $pixel->getColorCount() / $area; |
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// A common way of representing entropy in scalar |
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$value += $p * log($p, 2); |
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} |
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// $value is always 0.0 or negative, so transform into positive scalar value |
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return -$value; |
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} |
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public function getVerticalSlice($x, $sliceSize) |
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{ |
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$size = $this->image->getImageGeometry(); |
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return $this->getRegion($sliceSize, $size['height'], $x, 0); |
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} |
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public function getHorizontalSlice($y, $sliceSize) |
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{ |
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$size = $this->image->getImageGeometry(); |
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return $this->getRegion($size['width'], $sliceSize, 0, $y); |
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} |
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} |
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stojg /
crop
