Binarizer::calculateThresholdForBlock() - Code Metrics - chillerlan/php-qrcode - Measure and Improve Code Quality continuously with Scrutinizer

Binarizer::calculateThresholdForBlock() B
last analyzed 2023-06-21 14:22 UTC

↳ Parent: Binarizer

Complexity

Conditions	8
Paths	27

Size

Total Lines	44
Code Lines	24

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	0	Features	0

Metric	Value
cc	8
eloc	24
nc	27
nop	4
dl	0
loc	44
rs	8.4444
c	1
b	0
f	0

<?php
/**
 * Class Binarizer
 *
 * @created      17.01.2021
 * @author       ZXing Authors
 * @author       Smiley <[email protected]>
 * @copyright    2021 Smiley
 * @license      Apache-2.0
 */

namespace chillerlan\QRCode\Decoder;

use chillerlan\QRCode\Data\QRMatrix;
use function array_fill, count, max;

/**
 * This class implements a local thresholding algorithm, which while slower than the
 * GlobalHistogramBinarizer, is fairly efficient for what it does. It is designed for
 * high frequency images of barcodes with black data on white backgrounds. For this application,
 * it does a much better job than a global blackpoint with severe shadows and gradients.
 * However, it tends to produce artifacts on lower frequency images and is therefore not
 * a good general purpose binarizer for uses outside ZXing.
 *
 * This class extends GlobalHistogramBinarizer, using the older histogram approach for 1D readers,
 * and the newer local approach for 2D readers. 1D decoding using a per-row histogram is already
 * inherently local, and only fails for horizontal gradients. We can revisit that problem later,
 * but for now it was not a win to use local blocks for 1D.
 *
 * This Binarizer is the default for the unit tests and the recommended class for library users.
 *
 * @author [email protected] (Daniel Switkin)
 */
final class Binarizer{

	// This class uses 5x5 blocks to compute local luminance, where each block is 8x8 pixels.
	// So this is the smallest dimension in each axis we can accept.
	private const BLOCK_SIZE_POWER  = 3;
	private const BLOCK_SIZE        = 8;  // ...0100...00
	private const BLOCK_SIZE_MASK   = 7;  // ...0011...11
	private const MINIMUM_DIMENSION = 40;
	private const MIN_DYNAMIC_RANGE = 24;

#	private const LUMINANCE_BITS    = 5;
	private const LUMINANCE_SHIFT   = 3;
	private const LUMINANCE_BUCKETS = 32;

	private LuminanceSourceInterface $source;
	private array                    $luminances;

	/**
	 *
	 */
	public function __construct(LuminanceSourceInterface $source){
		$this->source     = $source;
		$this->luminances = $this->source->getLuminances();
	}

	/**
	 * @throws \chillerlan\QRCode\Decoder\QRCodeDecoderException
	 */
	private function estimateBlackPoint(array $buckets):int{
		// 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 new QRCodeDecoderException('no meaningful dark point found'); // @codeCoverageIgnore
		}

		// 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);
	}

	/**
	 * Calculates the final BitMatrix once for all requests. This could be called once from the
	 * constructor instead, but there are some advantages to doing it lazily, such as making
	 * profiling easier, and not doing heavy lifting when callers don't expect it.
	 *
	 * Converts a 2D array of luminance data to 1 bit data. As above, assume this method is expensive
	 * and do not call it repeatedly. This method is intended for decoding 2D barcodes and may or
	 * may not apply sharpening. Therefore, a row from this matrix may not be identical to one
	 * fetched using getBlackRow(), so don't mix and match between them.
	 *
	 * @return \chillerlan\QRCode\Decoder\BitMatrix The 2D array of bits for the image (true means black).
	 */
	public function getBlackMatrix():BitMatrix{
		$width  = $this->source->getWidth();
		$height = $this->source->getHeight();

		if($width >= self::MINIMUM_DIMENSION && $height >= self::MINIMUM_DIMENSION){
			$subWidth = ($width >> self::BLOCK_SIZE_POWER);

			if(($width & self::BLOCK_SIZE_MASK) !== 0){
				$subWidth++;
			}

			$subHeight = ($height >> self::BLOCK_SIZE_POWER);

			if(($height & self::BLOCK_SIZE_MASK) !== 0){
				$subHeight++;
			}

			return $this->calculateThresholdForBlock($subWidth, $subHeight, $width, $height);
		}

		// If the image is too small, fall back to the global histogram approach.
		return $this->getHistogramBlackMatrix($width, $height);
	}

	/**
	 *
	 */
	private function getHistogramBlackMatrix(int $width, int $height):BitMatrix{

		// 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.
		$buckets = array_fill(0, self::LUMINANCE_BUCKETS, 0);

		for($y = 1; $y < 5; $y++){
			$row             = (int)($height * $y / 5);
			$localLuminances = $this->source->getRow($row);
			$right           = (int)(($width * 4) / 5);

			for($x = (int)($width / 5); $x < $right; $x++){
				$pixel = ($localLuminances[$x] & 0xff);
				$buckets[($pixel >> self::LUMINANCE_SHIFT)]++;
			}
		}

		$blackPoint = $this->estimateBlackPoint($buckets);

		// 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.
		$matrix = new BitMatrix(max($width, $height));

		for($y = 0; $y < $height; $y++){
			$offset = ($y * $width);

			for($x = 0; $x < $width; $x++){
				$matrix->set($x, $y, (($this->luminances[($offset + $x)] & 0xff) < $blackPoint), QRMatrix::M_DATA);
			}
		}

		return $matrix;
	}

	/**
	 * Calculates a single black point for each block of pixels and saves it away.
	 * See the following thread for a discussion of this algorithm:
	 *
	 * @see http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
	 */
	private function calculateBlackPoints(int $subWidth, int $subHeight, int $width, int $height):array{
		$blackPoints = array_fill(0, $subHeight, array_fill(0, $subWidth, 0));

		for($y = 0; $y < $subHeight; $y++){
			$yoffset    = ($y << self::BLOCK_SIZE_POWER);
			$maxYOffset = ($height - self::BLOCK_SIZE);

			if($yoffset > $maxYOffset){
				$yoffset = $maxYOffset;
			}

			for($x = 0; $x < $subWidth; $x++){
				$xoffset    = ($x << self::BLOCK_SIZE_POWER);
				$maxXOffset = ($width - self::BLOCK_SIZE);

				if($xoffset > $maxXOffset){
					$xoffset = $maxXOffset;
				}

				$sum = 0;
				$min = 255;
				$max = 0;

				for($yy = 0, $offset = ($yoffset * $width + $xoffset); $yy < self::BLOCK_SIZE; $yy++, $offset += $width){

					for($xx = 0; $xx < self::BLOCK_SIZE; $xx++){
						$pixel = ((int)($this->luminances[(int)($offset + $xx)]) & 0xff);
						$sum   += $pixel;
						// still looking for good contrast
						if($pixel < $min){
							$min = $pixel;
						}

						if($pixel > $max){
							$max = $pixel;
						}
					}

					// short-circuit min/max tests once dynamic range is met
					if(($max - $min) > self::MIN_DYNAMIC_RANGE){
						// finish the rest of the rows quickly
						for($yy++, $offset += $width; $yy < self::BLOCK_SIZE; $yy++, $offset += $width){
							for($xx = 0; $xx < self::BLOCK_SIZE; $xx++){
								$sum += ((int)($this->luminances[(int)($offset + $xx)]) & 0xff);
							}
						}
					}
				}

				// The default estimate is the average of the values in the block.
				$average = ($sum >> (self::BLOCK_SIZE_POWER * 2));

				if(($max - $min) <= self::MIN_DYNAMIC_RANGE){
					// If variation within the block is low, assume this is a block with only light or only
					// dark pixels. In that case we do not want to use the average, as it would divide this
					// low contrast area into black and white pixels, essentially creating data out of noise.
					//
					// The default assumption is that the block is light/background. Since no estimate for
					// the level of dark pixels exists locally, use half the min for the block.
					$average = (int)($min / 2);

					if($y > 0 && $x > 0){
						// Correct the "white background" assumption for blocks that have neighbors by comparing
						// the pixels in this block to the previously calculated black points. This is based on
						// the fact that dark barcode symbology is always surrounded by some amount of light
						// background for which reasonable black point estimates were made. The bp estimated at
						// the boundaries is used for the interior.

						// The (min < bp) is arbitrary but works better than other heuristics that were tried.
						$averageNeighborBlackPoint = (int)(
							($blackPoints[($y - 1)][$x] + (2 * $blackPoints[$y][($x - 1)]) + $blackPoints[($y - 1)][($x - 1)]) / 4
						);

						if($min < $averageNeighborBlackPoint){
							$average = $averageNeighborBlackPoint;
						}
					}
				}

				$blackPoints[$y][$x] = $average;
			}
		}

		return $blackPoints;
	}

	/**
	 * For each block in the image, calculate the average black point using a 5x5 grid
	 * of the surrounding blocks. Also handles the corner cases (fractional blocks are computed based
	 * on the last pixels in the row/column which are also used in the previous block).
	 */
	private function calculateThresholdForBlock(int $subWidth, int $subHeight, int $width, int $height):BitMatrix{
		$matrix      = new BitMatrix(max($width, $height));
		$blackPoints = $this->calculateBlackPoints($subWidth, $subHeight, $width, $height);

		for($y = 0; $y < $subHeight; $y++){
			$yoffset    = ($y << self::BLOCK_SIZE_POWER);
			$maxYOffset = ($height - self::BLOCK_SIZE);

			if($yoffset > $maxYOffset){
				$yoffset = $maxYOffset;
			}

			for($x = 0; $x < $subWidth; $x++){
				$xoffset    = ($x << self::BLOCK_SIZE_POWER);
				$maxXOffset = ($width - self::BLOCK_SIZE);

				if($xoffset > $maxXOffset){
					$xoffset = $maxXOffset;
				}

				$left = $this->cap($x, 2, ($subWidth - 3));
				$top  = $this->cap($y, 2, ($subHeight - 3));
				$sum  = 0;

				for($z = -2; $z <= 2; $z++){
					$br   = $blackPoints[($top + $z)];
					$sum += ($br[($left - 2)] + $br[($left - 1)] + $br[$left] + $br[($left + 1)] + $br[($left + 2)]);
				}

				$average = (int)($sum / 25);

				// Applies a single threshold to a block of pixels.
				for($j = 0, $o = ($yoffset * $width + $xoffset); $j < self::BLOCK_SIZE; $j++, $o += $width){
					for($i = 0; $i < self::BLOCK_SIZE; $i++){
						// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0.
						$v = (((int)($this->luminances[($o + $i)]) & 0xff) <= $average);

						$matrix->set(($xoffset + $i), ($yoffset + $j), $v, QRMatrix::M_DATA);
					}
				}
			}
		}

		return $matrix;
	}

	/**
	 * @noinspection PhpSameParameterValueInspection
	 */
	private function cap(int $value, int $min, int $max):int{

		if($value < $min){
			return $min;
		}

		if($value > $max){
			return $max;
		}

		return $value;
	}

}


1			<?php
2			/**
3			* Class Binarizer
4			*
5			* @created 17.01.2021
6			* @author ZXing Authors
7			* @author Smiley <[email protected]>
8			* @copyright 2021 Smiley
9			* @license Apache-2.0
10			*/
11
12			namespace chillerlan\QRCode\Decoder;
13
14			use chillerlan\QRCode\Data\QRMatrix;
15			use function array_fill, count, max;
16
17			/**
18			* This class implements a local thresholding algorithm, which while slower than the
19			* GlobalHistogramBinarizer, is fairly efficient for what it does. It is designed for
20			* high frequency images of barcodes with black data on white backgrounds. For this application,
21			* it does a much better job than a global blackpoint with severe shadows and gradients.
22			* However, it tends to produce artifacts on lower frequency images and is therefore not
23			* a good general purpose binarizer for uses outside ZXing.
24			*
25			* This class extends GlobalHistogramBinarizer, using the older histogram approach for 1D readers,
26			* and the newer local approach for 2D readers. 1D decoding using a per-row histogram is already
27			* inherently local, and only fails for horizontal gradients. We can revisit that problem later,
28			* but for now it was not a win to use local blocks for 1D.
29			*
30			* This Binarizer is the default for the unit tests and the recommended class for library users.
31			*
32			* @author [email protected] (Daniel Switkin)
33			*/
34			final class Binarizer{
35
36			// This class uses 5x5 blocks to compute local luminance, where each block is 8x8 pixels.
37			// So this is the smallest dimension in each axis we can accept.
38			private const BLOCK_SIZE_POWER = 3;
39			private const BLOCK_SIZE = 8; // ...0100...00
40			private const BLOCK_SIZE_MASK = 7; // ...0011...11
41			private const MINIMUM_DIMENSION = 40;
42			private const MIN_DYNAMIC_RANGE = 24;
43
44			# private const LUMINANCE_BITS = 5;
45			private const LUMINANCE_SHIFT = 3;
46			private const LUMINANCE_BUCKETS = 32;
47
48			private LuminanceSourceInterface $source;
49			private array $luminances;
50
51			/**
52			*
53			*/
54			public function __construct(LuminanceSourceInterface $source){
55			$this->source = $source;
56			$this->luminances = $this->source->getLuminances();
57			}
58
59			/**
60			* @throws \chillerlan\QRCode\Decoder\QRCodeDecoderException
61			*/
62			private function estimateBlackPoint(array $buckets):int{
63			// Find the tallest peak in the histogram.
64			$numBuckets = count($buckets);
65			$maxBucketCount = 0;
66			$firstPeak = 0;
67			$firstPeakSize = 0;
68
69			for($x = 0; $x < $numBuckets; $x++){
70
71			if($buckets[$x] > $firstPeakSize){
72			$firstPeak = $x;
73			$firstPeakSize = $buckets[$x];
74			}
75
76			if($buckets[$x] > $maxBucketCount){
77			$maxBucketCount = $buckets[$x];
78			}
79			}
80
81			// Find the second-tallest peak which is somewhat far from the tallest peak.
82			$secondPeak = 0;
83			$secondPeakScore = 0;
84
85			for($x = 0; $x < $numBuckets; $x++){
86			$distanceToBiggest = ($x - $firstPeak);
87			// Encourage more distant second peaks by multiplying by square of distance.
88			$score = ($buckets[$x] * $distanceToBiggest * $distanceToBiggest);
89
90			if($score > $secondPeakScore){
91			$secondPeak = $x;
92			$secondPeakScore = $score;
93			}
94			}
95
96			// Make sure firstPeak corresponds to the black peak.
97			if($firstPeak > $secondPeak){
98			$temp = $firstPeak;
99			$firstPeak = $secondPeak;
100			$secondPeak = $temp;
101			}
102
103			// If there is too little contrast in the image to pick a meaningful black point, throw rather
104			// than waste time trying to decode the image, and risk false positives.
105			if(($secondPeak - $firstPeak) <= ($numBuckets / 16)){
106			throw new QRCodeDecoderException('no meaningful dark point found'); // @codeCoverageIgnore
107			}
108
109			// Find a valley between them that is low and closer to the white peak.
110			$bestValley = ($secondPeak - 1);
111			$bestValleyScore = -1;
112
113			for($x = ($secondPeak - 1); $x > $firstPeak; $x--){
114			$fromFirst = ($x - $firstPeak);
115			$score = ($fromFirst * $fromFirst * ($secondPeak - $x) * ($maxBucketCount - $buckets[$x]));
116
117			if($score > $bestValleyScore){
118			$bestValley = $x;
119			$bestValleyScore = $score;
120			}
121			}
122
123			return ($bestValley << self::LUMINANCE_SHIFT);
124			}
125
126			/**
127			* Calculates the final BitMatrix once for all requests. This could be called once from the
128			* constructor instead, but there are some advantages to doing it lazily, such as making
129			* profiling easier, and not doing heavy lifting when callers don't expect it.
130			*
131			* Converts a 2D array of luminance data to 1 bit data. As above, assume this method is expensive
132			* and do not call it repeatedly. This method is intended for decoding 2D barcodes and may or
133			* may not apply sharpening. Therefore, a row from this matrix may not be identical to one
134			* fetched using getBlackRow(), so don't mix and match between them.
135			*
136			* @return \chillerlan\QRCode\Decoder\BitMatrix The 2D array of bits for the image (true means black).
137			*/
138			public function getBlackMatrix():BitMatrix{
139			$width = $this->source->getWidth();
140			$height = $this->source->getHeight();
141
142			if($width >= self::MINIMUM_DIMENSION && $height >= self::MINIMUM_DIMENSION){
143			$subWidth = ($width >> self::BLOCK_SIZE_POWER);
144
145			if(($width & self::BLOCK_SIZE_MASK) !== 0){
146			$subWidth++;
147			}
148
149			$subHeight = ($height >> self::BLOCK_SIZE_POWER);
150
151			if(($height & self::BLOCK_SIZE_MASK) !== 0){
152			$subHeight++;
153			}
154
155			return $this->calculateThresholdForBlock($subWidth, $subHeight, $width, $height);
156			}
157
158			// If the image is too small, fall back to the global histogram approach.
159			return $this->getHistogramBlackMatrix($width, $height);
160			}
161
162			/**
163			*
164			*/
165			private function getHistogramBlackMatrix(int $width, int $height):BitMatrix{
166
167			// Quickly calculates the histogram by sampling four rows from the image. This proved to be
168			// more robust on the blackbox tests than sampling a diagonal as we used to do.
169			$buckets = array_fill(0, self::LUMINANCE_BUCKETS, 0);
170
171			for($y = 1; $y < 5; $y++){
172			$row = (int)($height * $y / 5);
173			$localLuminances = $this->source->getRow($row);
174			$right = (int)(($width * 4) / 5);
175
176			for($x = (int)($width / 5); $x < $right; $x++){
177			$pixel = ($localLuminances[$x] & 0xff);
178			$buckets[($pixel >> self::LUMINANCE_SHIFT)]++;
179			}
180			}
181
182			$blackPoint = $this->estimateBlackPoint($buckets);
183
184			// We delay reading the entire image luminance until the black point estimation succeeds.
185			// Although we end up reading four rows twice, it is consistent with our motto of
186			// "fail quickly" which is necessary for continuous scanning.
187			$matrix = new BitMatrix(max($width, $height));
188
189			for($y = 0; $y < $height; $y++){
190			$offset = ($y * $width);
191
192			for($x = 0; $x < $width; $x++){
193			$matrix->set($x, $y, (($this->luminances[($offset + $x)] & 0xff) < $blackPoint), QRMatrix::M_DATA);
194			}
195			}
196
197			return $matrix;
198			}
199
200			/**
201			* Calculates a single black point for each block of pixels and saves it away.
202			* See the following thread for a discussion of this algorithm:
203			*
204			* @see http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
205			*/
206			private function calculateBlackPoints(int $subWidth, int $subHeight, int $width, int $height):array{
207			$blackPoints = array_fill(0, $subHeight, array_fill(0, $subWidth, 0));
208
209			for($y = 0; $y < $subHeight; $y++){
210			$yoffset = ($y << self::BLOCK_SIZE_POWER);
211			$maxYOffset = ($height - self::BLOCK_SIZE);
212
213			if($yoffset > $maxYOffset){
214			$yoffset = $maxYOffset;
215			}
216
217			for($x = 0; $x < $subWidth; $x++){
218			$xoffset = ($x << self::BLOCK_SIZE_POWER);
219			$maxXOffset = ($width - self::BLOCK_SIZE);
220
221			if($xoffset > $maxXOffset){
222			$xoffset = $maxXOffset;
223			}
224
225			$sum = 0;
226			$min = 255;
227			$max = 0;
228
229			for($yy = 0, $offset = ($yoffset * $width + $xoffset); $yy < self::BLOCK_SIZE; $yy++, $offset += $width){
230
231			for($xx = 0; $xx < self::BLOCK_SIZE; $xx++){
232			$pixel = ((int)($this->luminances[(int)($offset + $xx)]) & 0xff);
233			$sum += $pixel;
234			// still looking for good contrast
235			if($pixel < $min){
236			$min = $pixel;
237			}
238
239			if($pixel > $max){
240			$max = $pixel;
241			}
242			}
243
244			// short-circuit min/max tests once dynamic range is met
245			if(($max - $min) > self::MIN_DYNAMIC_RANGE){
246			// finish the rest of the rows quickly
247			for($yy++, $offset += $width; $yy < self::BLOCK_SIZE; $yy++, $offset += $width){
248			for($xx = 0; $xx < self::BLOCK_SIZE; $xx++){
249			$sum += ((int)($this->luminances[(int)($offset + $xx)]) & 0xff);
250			}
251			}
252			}
253			}
254
255			// The default estimate is the average of the values in the block.
256			$average = ($sum >> (self::BLOCK_SIZE_POWER * 2));
257
258			if(($max - $min) <= self::MIN_DYNAMIC_RANGE){
259			// If variation within the block is low, assume this is a block with only light or only
260			// dark pixels. In that case we do not want to use the average, as it would divide this
261			// low contrast area into black and white pixels, essentially creating data out of noise.
262			//
263			// The default assumption is that the block is light/background. Since no estimate for
264			// the level of dark pixels exists locally, use half the min for the block.
265			$average = (int)($min / 2);
266
267			if($y > 0 && $x > 0){
268			// Correct the "white background" assumption for blocks that have neighbors by comparing
269			// the pixels in this block to the previously calculated black points. This is based on
270			// the fact that dark barcode symbology is always surrounded by some amount of light
271			// background for which reasonable black point estimates were made. The bp estimated at
272			// the boundaries is used for the interior.
273
274			// The (min < bp) is arbitrary but works better than other heuristics that were tried.
275			$averageNeighborBlackPoint = (int)(
276			($blackPoints[($y - 1)][$x] + (2 * $blackPoints[$y][($x - 1)]) + $blackPoints[($y - 1)][($x - 1)]) / 4
277			);
278
279			if($min < $averageNeighborBlackPoint){
280			$average = $averageNeighborBlackPoint;
281			}
282			}
283			}
284
285			$blackPoints[$y][$x] = $average;
286			}
287			}
288
289			return $blackPoints;
290			}
291
292			/**
293			* For each block in the image, calculate the average black point using a 5x5 grid
294			* of the surrounding blocks. Also handles the corner cases (fractional blocks are computed based
295			* on the last pixels in the row/column which are also used in the previous block).
296			*/
297			private function calculateThresholdForBlock(int $subWidth, int $subHeight, int $width, int $height):BitMatrix{
298			$matrix = new BitMatrix(max($width, $height));
299			$blackPoints = $this->calculateBlackPoints($subWidth, $subHeight, $width, $height);
300
301			for($y = 0; $y < $subHeight; $y++){
302			$yoffset = ($y << self::BLOCK_SIZE_POWER);
303			$maxYOffset = ($height - self::BLOCK_SIZE);
304
305			if($yoffset > $maxYOffset){
306			$yoffset = $maxYOffset;
307			}
308
309			for($x = 0; $x < $subWidth; $x++){
310			$xoffset = ($x << self::BLOCK_SIZE_POWER);
311			$maxXOffset = ($width - self::BLOCK_SIZE);
312
313			if($xoffset > $maxXOffset){
314			$xoffset = $maxXOffset;
315			}
316
317			$left = $this->cap($x, 2, ($subWidth - 3));
318			$top = $this->cap($y, 2, ($subHeight - 3));
319			$sum = 0;
320
321			for($z = -2; $z <= 2; $z++){
322			$br = $blackPoints[($top + $z)];
323			$sum += ($br[($left - 2)] + $br[($left - 1)] + $br[$left] + $br[($left + 1)] + $br[($left + 2)]);
324			}
325
326			$average = (int)($sum / 25);
327
328			// Applies a single threshold to a block of pixels.
329			for($j = 0, $o = ($yoffset * $width + $xoffset); $j < self::BLOCK_SIZE; $j++, $o += $width){
330			for($i = 0; $i < self::BLOCK_SIZE; $i++){
331			// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0.
332			$v = (((int)($this->luminances[($o + $i)]) & 0xff) <= $average);
333
334			$matrix->set(($xoffset + $i), ($yoffset + $j), $v, QRMatrix::M_DATA);
335			}
336			}
337			}
338			}
339
340			return $matrix;
341			}
342
343			/**
344			* @noinspection PhpSameParameterValueInspection
345			*/
346			private function cap(int $value, int $min, int $max):int{
347
348			if($value < $min){
349			return $min;
350			}
351
352			if($value > $max){
353			return $max;
354			}
355
356			return $value;
357			}
358
359			}
360

chillerlan / php-qrcode

Binarizer::calculateThresholdForBlock() B last analyzed 2023-06-21 14:22 UTC

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Binarizer::calculateThresholdForBlock() B
last analyzed 2023-06-21 14:22 UTC