diff --git a/src/Common/MaskPattern.php b/src/Common/MaskPattern.php
index 9a57d1007..1c151cfe1 100644
--- a/src/Common/MaskPattern.php
+++ b/src/Common/MaskPattern.php
@@ -70,22 +70,28 @@ final class MaskPattern{
 	/**
 	 * Returns a closure that applies the mask for the chosen mask pattern.
 	 *
-	 * Note that some versions of the QR code standard have had errors in the section about mask patterns.
-	 * The information below has been corrected.
+	 * Encapsulates data masks for the data bits in a QR code, per ISO 18004:2006 6.8. Implementations
+	 * of this class can un-mask a raw BitMatrix. For simplicity, they will unmask the entire BitMatrix,
+	 * including areas used for finder patterns, timing patterns, etc. These areas should be unused
+	 * after the point they are unmasked anyway.
+	 *
+	 * Note that the diagram in section 6.8.1 is misleading since it indicates that i is column position
+	 * and j is row position. In fact, as the text says, i is row position and j is column position.
 	 *
 	 * @see https://www.thonky.com/qr-code-tutorial/mask-patterns
+	 * @see https://github.com/zxing/zxing/blob/e9e2bd280bcaeabd59d0f955798384fe6c018a6c/core/src/main/java/com/google/zxing/qrcode/decoder/DataMask.java#L32-L117
 	 */
 	public function getMask():Closure{
 		// $x = column (width), $y = row (height)
 		return [
-			self::PATTERN_000 => fn(int $x, int $y):int => ($x + $y) % 2,
-			self::PATTERN_001 => fn(int $x, int $y):int => $y % 2,
-			self::PATTERN_010 => fn(int $x, int $y):int => $x % 3,
-			self::PATTERN_011 => fn(int $x, int $y):int => ($x + $y) % 3,
-			self::PATTERN_100 => fn(int $x, int $y):int => ((int)($y / 2) + (int)($x / 3)) % 2,
-			self::PATTERN_101 => fn(int $x, int $y):int => (($x * $y) % 2) + (($x * $y) % 3),
-			self::PATTERN_110 => fn(int $x, int $y):int => ((($x * $y) % 2) + (($x * $y) % 3)) % 2,
-			self::PATTERN_111 => fn(int $x, int $y):int => ((($x * $y) % 3) + (($x + $y) % 2)) % 2,
+			self::PATTERN_000 => fn(int $x, int $y):bool => (($x + $y) % 2) === 0,
+			self::PATTERN_001 => fn(int $x, int $y):bool => ($y % 2) === 0,
+			self::PATTERN_010 => fn(int $x, int $y):bool => ($x % 3) === 0,
+			self::PATTERN_011 => fn(int $x, int $y):bool => (($x + $y) % 3) === 0,
+			self::PATTERN_100 => fn(int $x, int $y):bool => (((int)($y / 2) + (int)($x / 3)) % 2) === 0,
+			self::PATTERN_101 => fn(int $x, int $y):bool => ($x * $y) % 6 === 0, // ((($x * $y) % 2) + (($x * $y) % 3)) === 0,
+			self::PATTERN_110 => fn(int $x, int $y):bool => (($x * $y) % 6) < 3, // (((($x * $y) % 2) + (($x * $y) % 3)) % 2) === 0,
+			self::PATTERN_111 => fn(int $x, int $y):bool => (($x + $y + (($x * $y) % 3)) % 2) === 0, // (((($x * $y) % 3) + (($x + $y) % 2)) % 2) === 0,
 		][$this->maskPattern];
 	}
 
diff --git a/src/Common/MaskPatternTester.php b/src/Common/MaskPatternTester.php
index 1a0549064..c35203c7e 100644
--- a/src/Common/MaskPatternTester.php
+++ b/src/Common/MaskPatternTester.php
@@ -72,7 +72,8 @@ final class MaskPatternTester{
 	}
 
 	/**
-	 * Checks for each group of five or more same-colored modules in a row (or column)
+	 * Apply mask penalty rule 1 and return the penalty. Find repetitive cells with the same color and
+	 * give penalty to them. Example: 00000 or 11111.
 	 */
 	private function testLevel1(array $m, int $size):int{
 		$penalty = 0;
@@ -111,7 +112,9 @@ final class MaskPatternTester{
 	}
 
 	/**
-	 * Checks for each 2x2 area of same-colored modules in the matrix
+	 * Apply mask penalty rule 2 and return the penalty. Find 2x2 blocks with the same color and give
+	 * penalty to them. This is actually equivalent to the spec's rule, which is to find MxN blocks and give a
+	 * penalty proportional to (M-1)x(N-1), because this is the number of 2x2 blocks inside such a block.
 	 */
 	private function testLevel2(array $m, int $size):int{
 		$penalty = 0;
@@ -142,7 +145,9 @@ final class MaskPatternTester{
 	}
 
 	/**
-	 * Checks if there are patterns that look similar to the finder patterns (1:1:3:1:1 ratio)
+	 * Apply mask penalty rule 3 and return the penalty. Find consecutive runs of 1:1:3:1:1:4
+	 * starting with black, or 4:1:1:3:1:1 starting with white, and give penalty to them.  If we
+	 * find patterns like 000010111010000, we give penalty once.
 	 */
 	private function testLevel3(array $m, int $size):int{
 		$penalties = 0;
@@ -183,7 +188,8 @@ final class MaskPatternTester{
 	}
 
 	/**
-	 * Checks if more than half of the modules are dark or light, with a larger penalty for a larger difference
+	 * Apply mask penalty rule 4 and return the penalty. Calculate the ratio of dark cells and give
+	 * penalty if the ratio is far from 50%. It gives 10 penalty for 5% distance.
 	 */
 	private function testLevel4(array $m, int $size):float{
 		$count = 0;
diff --git a/src/Data/QRMatrix.php b/src/Data/QRMatrix.php
index 6bf7c05bd..dd0a04ff9 100755
--- a/src/Data/QRMatrix.php
+++ b/src/Data/QRMatrix.php
@@ -571,7 +571,7 @@ final class QRMatrix{
 
 		foreach($this->matrix as $y => &$row){
 			foreach($row as $x => &$val){
-				if($mask($x, $y) === 0 && ($val & $this::M_DATA) === $this::M_DATA){
+				if($mask($x, $y) && ($val & $this::M_DATA) === $this::M_DATA){
 					$val ^= $this::IS_DARK;
 				}
 			}
diff --git a/src/Decoder/BitMatrix.php b/src/Decoder/BitMatrix.php
index 4863d8e1f..11201d3ef 100644
--- a/src/Decoder/BitMatrix.php
+++ b/src/Decoder/BitMatrix.php
@@ -182,23 +182,15 @@ final class BitMatrix{
 	}
 
 	/**
-	 * <p>Encapsulates data masks for the data bits in a QR code, per ISO 18004:2006 6.8. Implementations
-	 * of this class can un-mask a raw BitMatrix. For simplicity, they will unmask the entire BitMatrix,
-	 * including areas used for finder patterns, timing patterns, etc. These areas should be unused
-	 * after the point they are unmasked anyway.</p>
-	 *
-	 * <p>Note that the diagram in section 6.8.1 is misleading since it indicates that i is column position
-	 * and j is row position. In fact, as the text says, i is row position and j is column position.</p>
-	 *
-	 * <p>Implementations of this method reverse the data masking process applied to a QR Code and
-	 * make its bits ready to read.</p>
+	 * Implementations of this method reverse the data masking process applied to a QR Code and
+	 * make its bits ready to read.
 	 */
 	public function unmask(int $dimension, MaskPattern $maskPattern):void{
 		$mask = $maskPattern->getMask();
 
 		for($y = 0; $y < $dimension; $y++){
 			for($x = 0; $x < $dimension; $x++){
-				if($mask($x, $y) === 0){
+				if($mask($x, $y)){
 					$this->flip($x, $y);
 				}
 			}