You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
264 lines
11 KiB
264 lines
11 KiB
<?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 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 dswitkin@google.com (Daniel Switkin)
|
|
*/
|
|
final class HybridBinarizer extends GlobalHistogramBinarizer
|
|
{
|
|
|
|
// 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 static $BLOCK_SIZE_POWER = 3;
|
|
private static $BLOCK_SIZE = 8; // ...0100...00
|
|
private static $BLOCK_SIZE_MASK = 7; // ...0011...11
|
|
private static $MINIMUM_DIMENSION = 40;
|
|
private static $MIN_DYNAMIC_RANGE = 24;
|
|
|
|
private $matrix;
|
|
|
|
public function __construct($source)
|
|
{
|
|
parent::__construct($source);
|
|
self::$BLOCK_SIZE_POWER = 3;
|
|
self::$BLOCK_SIZE = 1 << self::$BLOCK_SIZE_POWER; // ...0100...00
|
|
self::$BLOCK_SIZE_MASK = self::$BLOCK_SIZE - 1; // ...0011...11
|
|
self::$MINIMUM_DIMENSION = self::$BLOCK_SIZE * 5;
|
|
self::$MIN_DYNAMIC_RANGE = 24;
|
|
}
|
|
|
|
/**
|
|
* Calculates the final BitMatrix once for all requests. This could be called once from the
|
|
* constructor instead, but there are some advantages to doing it lazily, such as making
|
|
* profiling easier, and not doing heavy lifting when callers don't expect it.
|
|
*/
|
|
public function getBlackMatrix()
|
|
{
|
|
if ($this->matrix !== null) {
|
|
return $this->matrix;
|
|
}
|
|
$source = $this->getLuminanceSource();
|
|
$width = $source->getWidth();
|
|
$height = $source->getHeight();
|
|
if ($width >= self::$MINIMUM_DIMENSION && $height >= self::$MINIMUM_DIMENSION) {
|
|
$luminances = $source->getMatrix();
|
|
$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++;
|
|
}
|
|
$blackPoints = self::calculateBlackPoints($luminances, $subWidth, $subHeight, $width, $height);
|
|
|
|
$newMatrix = new BitMatrix($width, $height);
|
|
self::calculateThresholdForBlock($luminances, $subWidth, $subHeight, $width, $height, $blackPoints, $newMatrix);
|
|
$this->matrix = $newMatrix;
|
|
} else {
|
|
// If the image is too small, fall back to the global histogram approach.
|
|
$this->matrix = parent::getBlackMatrix();
|
|
}
|
|
|
|
return $this->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:
|
|
* http://groups.google.com/group/zxing/browse_thread/thread/d06efa2c35a7ddc0
|
|
*/
|
|
private static function calculateBlackPoints(
|
|
$luminances,
|
|
$subWidth,
|
|
$subHeight,
|
|
$width,
|
|
$height
|
|
) {
|
|
$blackPoints = fill_array(0, $subHeight, 0);
|
|
foreach ($blackPoints as $key => $point) {
|
|
$blackPoints[$key] = fill_array(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 = 0xFF;
|
|
$max = 0;
|
|
for ($yy = 0, $offset = $yoffset * $width + $xoffset; $yy < self::$BLOCK_SIZE; $yy++, $offset += $width) {
|
|
for ($xx = 0; $xx < self::$BLOCK_SIZE; $xx++) {
|
|
$pixel = ((int)($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++) {
|
|
$sum += ($luminances[$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][$x] = (int)($average);
|
|
}
|
|
}
|
|
|
|
return $blackPoints;
|
|
}
|
|
|
|
/**
|
|
* For each block in the image, calculate the average black point using a 5x5 grid
|
|
* of the blocks around it. 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 static function calculateThresholdForBlock(
|
|
$luminances,
|
|
$subWidth,
|
|
$subHeight,
|
|
$width,
|
|
$height,
|
|
$blackPoints,
|
|
$matrix
|
|
) {
|
|
for ($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;
|
|
}
|
|
$left = self::cap($x, 2, $subWidth - 3);
|
|
$top = self::cap($y, 2, $subHeight - 3);
|
|
$sum = 0;
|
|
for ($z = -2; $z <= 2; $z++) {
|
|
$blackRow = $blackPoints[$top + $z];
|
|
$sum += $blackRow[$left - 2] + $blackRow[$left - 1] + $blackRow[$left] + $blackRow[$left + 1] + $blackRow[$left + 2];
|
|
}
|
|
$average = (int)($sum / 25);
|
|
|
|
self::thresholdBlock($luminances, $xoffset, $yoffset, $average, $width, $matrix);
|
|
}
|
|
}
|
|
}
|
|
|
|
private static function cap($value, $min, $max)
|
|
{
|
|
if ($value < $min) {
|
|
return $min;
|
|
} elseif ($value > $max) {
|
|
return $max;
|
|
} else {
|
|
return $value;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Applies a single threshold to a block of pixels.
|
|
*/
|
|
private static function thresholdBlock(
|
|
$luminances,
|
|
$xoffset,
|
|
$yoffset,
|
|
$threshold,
|
|
$stride,
|
|
$matrix
|
|
) {
|
|
|
|
for ($y = 0, $offset = $yoffset * $stride + $xoffset; $y < self::$BLOCK_SIZE; $y++, $offset += $stride) {
|
|
for ($x = 0; $x < self::$BLOCK_SIZE; $x++) {
|
|
// Comparison needs to be <= so that black == 0 pixels are black even if the threshold is 0.
|
|
if (($luminances[$offset + $x] & 0xFF) <= $threshold) {
|
|
$matrix->set($xoffset + $x, $yoffset + $y);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
public function createBinarizer($source)
|
|
{
|
|
return new HybridBinarizer($source);
|
|
}
|
|
}
|
|
|