chillerlan\QRCode\Decoder\Binarizer::calculateBlackPoints()

Complexity

Conditions	17
Paths	358

Size

Total Lines	86
Code Lines	37

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	0	Features	0

<?php
	private function calculateBlackPoints(array $luminances, int $subWidth, int $subHeight, int $width, int $height):array{
		$blackPoints = array_fill(0, $subHeight, 0);

		foreach($blackPoints as $key => $point){
			$blackPoints[$key] = 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++){
						$pixel = (int)($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;
	}