/**
* 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++) {
$yoffset = intval32bits($y << self::$BLOCK_SIZE_POWER);
$maxYOffset = $height - self::$BLOCK_SIZE;
if ($yoffset > $maxYOffset) {
$yoffset = $maxYOffset;
}
for ($x = 0; $x < $subWidth; $x++) {
$xoffset = intval32bits($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++) {
$pixel = intval32bits(intval($luminances[intval($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++) {
$sum += intval32bits($luminances[$offset + $xx] & 0xff);
}
}
}
}
// The default estimate is the average of the values in the block.
$average = intval32bits($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.
$average = intval($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.
$averageNeighborBlackPoint = intval(($blackPoints[$y - 1][$x] + 2 * $blackPoints[$y][$x - 1] + $blackPoints[$y - 1][$x - 1]) / 4);
if ($min < $averageNeighborBlackPoint) {
$average = $averageNeighborBlackPoint;
}
}
}
$blackPoints[$y][$x] = intval($average);
}
}
return $blackPoints;
}
public function renderThumbnail()
{
$width = intval($this->getWidth() / self::$THUMBNAIL_SCALE_FACTOR);
$height = intval($this->getHeight() / self::$THUMBNAIL_SCALE_FACTOR);
$pixels = array();
//new int[width * height];
$yuv = $this->yuvData;
$inputOffset = $this->top * $this->dataWidth + $this->left;
for ($y = 0; $y < $height; $y++) {
$outputOffset = $y * $width;
for ($x = 0; $x < $width; $x++) {
$grey = intval32bits($yuv[$inputOffset + $x * self::$THUMBNAIL_SCALE_FACTOR] & 0xff);
$pixels[$outputOffset + $x] = intval32bits(0xff000000 | $grey * 0x10101);
}
$inputOffset += $this->dataWidth * self::$THUMBNAIL_SCALE_FACTOR;
}
return $pixels;
}
/**
* @param $i; bit to get
* @return true iff bit i is set
*/
public function get($i)
{
$key = intval($i / 32);
return intval32bits($this->bits[$key] & 1 << ($i & 0x1f)) != 0;
}
private static function estimateBlackPoint($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);
}