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✏️ Editing: GlobalHistogramBinarizer.php

<?php
/*
* Copyright 2009 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

namespace  Zxing\Common;

use Zxing\Binarizer;
use Zxing\LuminanceSource;
use Zxing\NotFoundException;

/**
 * This Binarizer implementation uses the old ZXing global histogram approach. It is suitable
 * for low-end mobile devices which don't have enough CPU or memory to use a local thresholding
 * algorithm. However, because it picks a global black point, it cannot handle difficult shadows
 * and gradients.
 *
 * Faster mobile devices and all desktop applications should probably use HybridBinarizer instead.
 *
 * @author dswitkin@google.com (Daniel Switkin)
 * @author Sean Owen
 */

class GlobalHistogramBinarizer extends Binarizer {

private static $LUMINANCE_BITS = 5;
    private static $LUMINANCE_SHIFT=3;
    private static $LUMINANCE_BUCKETS = 32;

private static $EMPTY = array();

private $luminances=array();
    private $buckets = array();
    private $source = array();

public function __construct($source) {

self::$LUMINANCE_SHIFT = 8 - self::$LUMINANCE_BITS;
        self::$LUMINANCE_BUCKETS = 1 << self::$LUMINANCE_BITS;

parent::__construct($source);

$this->luminances = self::$EMPTY;
        $this->buckets = fill_array(0, self::$LUMINANCE_BUCKETS,0);
        $this->source = $source;
    }

// Applies simple sharpening to the row data to improve performance of the 1D Readers.
//@Override
    public function getBlackRow($y, $row=null) {
        $this->source = $this->getLuminanceSource();
        $width = $this->source->getWidth();
        if ($row == null || $row->getSize() < $width) {
            $row = new BitArray($width);
        } else {
            $row->clear();
        }

$this->initArrays($width);
        $localLuminances = $this->source->getRow($y, $this->luminances);
        $localBuckets = $this->buckets;
        for ($x = 0; $x < $width; $x++) {
            $pixel = $localLuminances[$x] & 0xff;
            $localBuckets[$pixel >> self::$LUMINANCE_SHIFT]++;
        }
        $blackPoint = $this->estimateBlackPoint($localBuckets);

$left = $localLuminances[0] & 0xff;
        $center = $localLuminances[1] & 0xff;
        for ($x = 1; $x < $width - 1; $x++) {
            $right = $localLuminances[$x + 1] & 0xff;
// A simple -1 4 -1 box filter with a weight of 2.
            $luminance = (($center * 4) - $left - $right) / 2;
            if ($luminance < $blackPoint) {
                $row->set($x);
            }
            $left = $center;
            $center = $right;
        }
        return $row;
    }

// Does not sharpen the data, as this call is intended to only be used by 2D Readers.
//@Override
    public function getBlackMatrix(){
        $source = $this->getLuminanceSource();
        $width = $source->getWidth();
        $height = $source->getHeight();
        $matrix = new BitMatrix($width, $height);

// Quickly calculates the histogram by sampling four rows from the image. This proved to be
// more robust on the blackbox tests than sampling a diagonal as we used to do.
        $this->initArrays($width);
        $localBuckets = $this->buckets;
        for ($y = 1; $y < 5; $y++) {
            $row = intval($height * $y / 5);
            $localLuminances = $source->getRow($row, $this->luminances);
            $right = intval(($width * 4) / 5);
            for ($x = intval($width / 5); $x < $right; $x++) {
                $pixel = intval32bits($localLuminances[intval($x)] & 0xff);
                $localBuckets[intval32bits($pixel >> self::$LUMINANCE_SHIFT)]++;
            }
        }
        $blackPoint = $this->estimateBlackPoint($localBuckets);

// We delay reading the entire image luminance until the black point estimation succeeds.
// Although we end up reading four rows twice, it is consistent with our motto of
// "fail quickly" which is necessary for continuous scanning.
        $localLuminances = $source->getMatrix();
        for ($y = 0; $y < $height; $y++) {
            $offset = $y * $width;
            for ($x = 0; $x< $width; $x++) {
                $pixel = intval($localLuminances[$offset + $x] & 0xff);
                if ($pixel < $blackPoint) {
                    $matrix->set($x, $y);
                }
            }
        }

return $matrix;
    }

//@Override
    public function createBinarizer($source) {
        return new GlobalHistogramBinarizer($source);
    }

private function initArrays($luminanceSize) {
        if (count($this->luminances) < $luminanceSize) {
            $this->luminances = array();
        }
        for ($x = 0; $x < self::$LUMINANCE_BUCKETS; $x++) {
            $this->buckets[$x] = 0;
        }
    }

private static function estimateBlackPoint($buckets){
// Find the tallest peak in the histogram.
        $numBuckets = count($buckets);
        $maxBucketCount = 0;
        $firstPeak = 0;
        $firstPeakSize = 0;
        for ($x = 0; $x < $numBuckets; $x++) {
            if ($buckets[$x] > $firstPeakSize) {
                $firstPeak = $x;
                $firstPeakSize = $buckets[$x];
            }
            if ($buckets[$x] > $maxBucketCount) {
                $maxBucketCount = $buckets[$x];
            }
        }

// Find the second-tallest peak which is somewhat far from the tallest peak.
        $secondPeak = 0;
        $secondPeakScore = 0;
        for ($x = 0; $x < $numBuckets; $x++) {
            $distanceToBiggest = $x - $firstPeak;
// Encourage more distant second peaks by multiplying by square of distance.
            $score = $buckets[$x] * $distanceToBiggest * $distanceToBiggest;
            if ($score > $secondPeakScore) {
                $secondPeak = $x;
                $secondPeakScore = $score;
            }
        }

// Make sure firstPeak corresponds to the black peak.
        if ($firstPeak > $secondPeak) {
            $temp = $firstPeak;
            $firstPeak = $secondPeak;
            $secondPeak = $temp;
        }

// If there is too little contrast in the image to pick a meaningful black point, throw rather
// than waste time trying to decode the image, and risk false positives.
        if ($secondPeak - $firstPeak <= $numBuckets / 16) {
           throw NotFoundException::getNotFoundInstance();
        }

// Find a valley between them that is low and closer to the white peak.
        $bestValley = $secondPeak - 1;
        $bestValleyScore = -1;
        for ($x = $secondPeak - 1; $x > $firstPeak; $x--) {
            $fromFirst = $x - $firstPeak;
            $score = $fromFirst * $fromFirst * ($secondPeak - $x) * ($maxBucketCount - $buckets[$x]);
            if ($score > $bestValleyScore) {
                $bestValley = $x;
                $bestValleyScore = $score;
            }
        }

return intval32bits($bestValley << self::$LUMINANCE_SHIFT);
    }

}

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