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Improving robustness of Code 128 decoder; Relates to #104
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@serratus
serratus committed Apr 17, 2016
1 parent 9c21283 commit 7a9f146
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Showing 2 changed files with 67 additions and 29 deletions.
43 changes: 22 additions & 21 deletions src/reader/barcode_reader.js
View file
Original file line number Diff line number Diff line change
Expand Up @@ -47,41 +47,42 @@ BarcodeReader.prototype._nextSet = function(line, offset) {
return line.length;
};

BarcodeReader.prototype._normalize = function(counter, modulo) {
BarcodeReader.prototype._normalize = function(counter, correction) {
var i,
self = this,
sum = 0,
ratio,
numOnes = 0,
normalized = [],
norm = 0;

if (!modulo) {
normalized = new Array(counter.length),
norm = 0,
modulo = self.MODULO;

if (correction) {
correct(counter, correction.bar, [0, 2, 4]);
correct(counter, correction.space, [1, 3, 5]);
}
for (i = 0; i < counter.length; i++) {
if (counter[i] === 1) {
numOnes++;
} else {
sum += counter[i];
}
sum += counter[i];
}
ratio = sum / (modulo - numOnes);
if (ratio > 1.0) {
for (i = 0; i < counter.length; i++) {
norm = counter[i] === 1 ? counter[i] : counter[i] / ratio;
normalized.push(norm);
}
} else {
ratio = (sum + numOnes) / modulo;
for (i = 0; i < counter.length; i++) {
norm = counter[i] / ratio;
normalized.push(norm);
}
for (i = 0; i < counter.length; i++) {
norm = counter[i] === 1 ? counter[i] : counter[i] / ratio;
normalized[i] = norm;
}
return normalized;
};

function correct(counter, correction, indices) {
var length = indices.length,
tmp = 0;
while(length--) {
tmp = counter[indices[length]] * (1 - ((1 - correction) / 2));
if (tmp > 1) {
counter[indices[length]] = tmp;
}
}
}

BarcodeReader.prototype._matchTrace = function(cmpCounter, epsilon) {
var counter = [],
i,
Expand Down
53 changes: 45 additions & 8 deletions src/reader/code_128_reader.js
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Original file line number Diff line number Diff line change
Expand Up @@ -123,15 +123,15 @@ var properties = {
[2, 1, 1, 2, 3, 2],
[2, 3, 3, 1, 1, 1, 2]
]},
SINGLE_CODE_ERROR: {value: 1},
AVG_CODE_ERROR: {value: 0.5},
SINGLE_CODE_ERROR: {value: 0.64},
AVG_CODE_ERROR: {value: 0.30},
FORMAT: {value: "code_128", writeable: false}
};

Code128Reader.prototype = Object.create(BarcodeReader.prototype, properties);
Code128Reader.prototype.constructor = Code128Reader;

Code128Reader.prototype._decodeCode = function(start) {
Code128Reader.prototype._decodeCode = function(start, correction) {
var counter = [0, 0, 0, 0, 0, 0],
i,
self = this,
Expand All @@ -142,7 +142,11 @@ Code128Reader.prototype._decodeCode = function(start) {
error: Number.MAX_VALUE,
code: -1,
start: start,
end: start
end: start,
correction: {
bar: 1,
space: 1
}
},
code,
error,
Expand All @@ -153,7 +157,7 @@ Code128Reader.prototype._decodeCode = function(start) {
counter[counterPos]++;
} else {
if (counterPos === counter.length - 1) {
normalized = self._normalize(counter);
normalized = self._normalize(counter, correction);
if (normalized) {
for (code = 0; code < self.CODE_PATTERN.length; code++) {
error = self._matchPattern(normalized, self.CODE_PATTERN[code]);
Expand All @@ -163,6 +167,15 @@ Code128Reader.prototype._decodeCode = function(start) {
}
}
bestMatch.end = i;
if (bestMatch.code === -1) {
return null;
}
if (self.CODE_PATTERN[bestMatch.code]) {
bestMatch.correction.bar = calculateCorrection(
self.CODE_PATTERN[bestMatch.code], normalized, [0, 2, 4]);
bestMatch.correction.space = calculateCorrection(
self.CODE_PATTERN[bestMatch.code], normalized, [1, 3, 5]);
}
return bestMatch;
}
} else {
Expand All @@ -175,6 +188,18 @@ Code128Reader.prototype._decodeCode = function(start) {
return null;
};

function calculateCorrection(expected, normalized, indices) {
var length = indices.length,
sumNormalized = 0,
sumExpected = 0;

while(length--) {
sumExpected += expected[indices[length]];
sumNormalized += normalized[indices[length]];
}
return sumExpected/sumNormalized;
}

Code128Reader.prototype._findStart = function() {
var counter = [0, 0, 0, 0, 0, 0],
i,
Expand All @@ -186,7 +211,11 @@ Code128Reader.prototype._findStart = function() {
error: Number.MAX_VALUE,
code: -1,
start: 0,
end: 0
end: 0,
correction: {
bar: 1,
space: 1
}
},
code,
error,
Expand Down Expand Up @@ -215,6 +244,10 @@ Code128Reader.prototype._findStart = function() {
if (bestMatch.error < self.AVG_CODE_ERROR) {
bestMatch.start = i - sum;
bestMatch.end = i;
bestMatch.correction.bar = calculateCorrection(
self.CODE_PATTERN[code], normalized, [0, 2, 4]);
bestMatch.correction.space = calculateCorrection(
self.CODE_PATTERN[code], normalized, [1, 3, 5]);
return bestMatch;
}
}
Expand Down Expand Up @@ -256,7 +289,11 @@ Code128Reader.prototype._decode = function() {
code = {
code: startInfo.code,
start: startInfo.start,
end: startInfo.end
end: startInfo.end,
correction: {
bar: startInfo.correction.bar,
space: startInfo.correction.space
}
};
decodedCodes.push(code);
checksum = code.code;
Expand All @@ -277,7 +314,7 @@ Code128Reader.prototype._decode = function() {
while (!done) {
unshift = shiftNext;
shiftNext = false;
code = self._decodeCode(code.end);
code = self._decodeCode(code.end, code.correction);
if (code !== null) {
if (code.code !== self.STOP_CODE) {
removeLastCharacter = true;
Expand Down

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