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<?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 = []; private $luminances = []; private $buckets = []; private $source = []; public function __construct($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 = $source; } // Applies simple sharpening to the row data to improve performance of the 1D Readers. public function getBlackRow($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]++; } $blackPoint = self::estimateBlackPoint($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 $row; } // Does not sharpen the data, as this call is intended to only be used by 2D Readers. private function initArrays($luminanceSize) { if (count($this->luminances) < $luminanceSize) { $this->luminances = []; } for ($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 = $score; } } return ($bestValley << self::$LUMINANCE_SHIFT); } 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++) { $row = (int)($height * $y / 5); $localLuminances = $source->getRow($row, $this->luminances); $right = (int)(($width * 4) / 5); for ($x = (int)($width / 5); $x < $right; $x++) { $pixel = ($localLuminances[(int)($x)] & 0xff); $localBuckets[($pixel >> self::$LUMINANCE_SHIFT)]++; } } $blackPoint = self::estimateBlackPoint($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++) { $pixel = (int)($localLuminances[$offset + $x] & 0xff); if ($pixel < $blackPoint) { $matrix->set($x, $y); } } } return $matrix; } public function createBinarizer($source) { return new GlobalHistogramBinarizer($source); } }
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