Decodes Code 39 barcodes. This does not supported "Full ASCII Code 39" yet.
+ *Decodes Code 39 barcodes. This does not support "Full ASCII Code 39" yet.
* * @author srowen@google.com (Sean Owen) */ @@ -32,10 +35,15 @@ public final class Code39Reader extends AbstractOneDReader { private static final String ALPHABET_STRING = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. *$/+%"; private static final char[] ALPHABET = ALPHABET_STRING.toCharArray(); + /** + * These represent the encodings of characters, as patterns of wide and narrow bars. + * The 9 least-significant bits of each int correspond to the pattern of wide and narrow, + * with 1s representing "wide" and 0s representing narrow. + */ private static final int[] CHARACTER_ENCODINGS = { - 0x038, 0x121, 0x061, 0x160, 0x031, 0x130, 0x070, 0x025, 0x124, 0x064, // 0-9 - 0x109, 0x049, 0x148, 0x019, 0x118, 0x058, 0x00D, 0x10C, 0x08C, 0x01C, // A-J - 0x103, 0x043, 0x142, 0x013, 0x112, 0x052, 0x007, 0x106, 0x046, 0x016, // K-T + 0x034, 0x121, 0x061, 0x160, 0x031, 0x130, 0x070, 0x025, 0x124, 0x064, // 0-9 + 0x109, 0x049, 0x148, 0x019, 0x118, 0x058, 0x00D, 0x10C, 0x04C, 0x01C, // A-J + 0x103, 0x043, 0x142, 0x013, 0x112, 0x052, 0x007, 0x106, 0x046, 0x016, // K-T 0x181, 0x0C1, 0x1C0, 0x091, 0x190, 0x0D0, 0x085, 0x184, 0x0C4, 0x094, // U-* 0x0A8, 0x0A2, 0x08A, 0x02A // $-% }; @@ -43,31 +51,48 @@ public final class Code39Reader extends AbstractOneDReader { private static final int ASTERISK_ENCODING = CHARACTER_ENCODINGS[39]; private final boolean usingCheckDigit; + private final boolean extendedMode; /** * Creates a reader that assumes all encoded data is data, and does not treat the final - * character as a check digit. + * character as a check digit. It will not decoded "extended Code 39" sequences. */ public Code39Reader() { usingCheckDigit = false; + extendedMode = false; } /** * Creates a reader that can be configured to check the last character as a check digit. + * It will not decoded "extended Code 39" sequences. * * @param usingCheckDigit if true, treat the last data character as a check digit, not - * data, and verify that the checksum passes + * data, and verify that the checksum passes. */ public Code39Reader(boolean usingCheckDigit) { this.usingCheckDigit = usingCheckDigit; + this.extendedMode = false; } - public Result decodeRow(final int rowNumber, final BitArray row) throws ReaderException { + /** + * Creates a reader that can be configured to check the last character as a check digit, + * or optionally attempt to decode "extended Code 39" sequences that are used to encode + * the full ASCII character set. + * + * @param usingCheckDigit if true, treat the last data character as a check digit, not + * data, and verify that the checksum passes. + * @param extendedMode if true, will attempt to decode extended Code 39 sequences in the + * text. + */ + public Code39Reader(boolean usingCheckDigit, boolean extendedMode) { + this.usingCheckDigit = usingCheckDigit; + this.extendedMode = extendedMode; + } - int[] start = findAsteriskPattern(row); + public Result decodeRow(int rowNumber, BitArray row, Hashtable hints) throws ReaderException { + int[] start = findAsteriskPattern(row); int nextStart = start[1]; - int end = row.getSize(); // Read off white space @@ -95,6 +120,18 @@ public final class Code39Reader extends AbstractOneDReader { } while (decodedChar != '*'); result.deleteCharAt(result.length() - 1); // remove asterisk + // Look for whitespace after pattern: + int lastPatternSize = 0; + for (int i = 0; i < counters.length; i++) { + lastPatternSize += counters[i]; + } + int whiteSpaceAfterEnd = nextStart - lastStart - lastPatternSize; + // If 50% of last pattern size, following last pattern, is not whitespace, fail + // (but if it's whitespace to the very end of the image, that's OK) + if (nextStart != end && whiteSpaceAfterEnd / 2 < lastPatternSize) { + throw new ReaderException("Pattern not followed by whitespace"); + } + if (usingCheckDigit) { int max = result.length() - 1; int total = 0; @@ -108,9 +145,24 @@ public final class Code39Reader extends AbstractOneDReader { } String resultString = result.toString(); - return new Result(resultString, - new ResultPoint[]{new GenericResultPoint((float) (start[1] - start[0]) / 2.0f, (float) rowNumber), - new GenericResultPoint((float) (nextStart - lastStart) / 2.0f, (float) rowNumber)}); + if (extendedMode) { + resultString = decodeExtended(resultString); + } + + if (resultString.length() == 0) { + // Almost surely a false positive + throw new ReaderException("Empty barcode found; assuming a false positive"); + } + + float left = (float) (start[1] + start[0]) / 2.0f; + float right = (float) (nextStart + lastStart) / 2.0f; + return new Result( + resultString, + null, + new ResultPoint[]{ + new GenericResultPoint(left, (float) rowNumber), + new GenericResultPoint(right, (float) rowNumber)}, + BarcodeFormat.CODE_39); } @@ -138,7 +190,10 @@ public final class Code39Reader extends AbstractOneDReader { if (counterPosition == patternLength - 1) { try { if (toNarrowWidePattern(counters) == ASTERISK_ENCODING) { - return new int[]{patternStart, i}; + // Look for whitespace before start pattern, >= 50% of width of start pattern + if (row.isRange(Math.max(0, patternStart - (i - patternStart) / 2), patternStart, false)) { + return new int[]{patternStart, i}; + } } } catch (ReaderException re) { // no match, continue @@ -147,6 +202,8 @@ public final class Code39Reader extends AbstractOneDReader { for (int y = 2; y < patternLength; y++) { counters[y - 2] = counters[y]; } + counters[patternLength - 2] = 0; + counters[patternLength - 1] = 0; counterPosition--; } else { counterPosition++; @@ -159,25 +216,47 @@ public final class Code39Reader extends AbstractOneDReader { } private static int toNarrowWidePattern(int[] counters) throws ReaderException { - int minCounter = Integer.MAX_VALUE; - for (int i = 0; i < counters.length; i++) { - if (counters[i] < minCounter) { - minCounter = counters[i]; + int numCounters = counters.length; + int maxNarrowCounter = 0; + int wideCounters; + do { + int minCounter = Integer.MAX_VALUE; + for (int i = 0; i < numCounters; i++) { + int counter = counters[i]; + if (counter < minCounter && counter > maxNarrowCounter) { + minCounter = counter; + } } - } - int maxNarrowCounter = (int) (minCounter * 1.5f); - int wideCounters = 0; - int pattern = 0; - for (int i = 0; i < counters.length; i++) { - if (counters[i] > maxNarrowCounter) { - pattern |= 1 << (counters.length - 1 - i); - wideCounters++; + maxNarrowCounter = minCounter; + wideCounters = 0; + int totalWideCountersWidth = 0; + int pattern = 0; + for (int i = 0; i < numCounters; i++) { + int counter = counters[i]; + if (counters[i] > maxNarrowCounter) { + pattern |= 1 << (numCounters - 1 - i); + wideCounters++; + totalWideCountersWidth += counter; + } } - } - if (wideCounters != 3) { - throw new ReaderException("Can't find 3 wide bars/spaces out of 9"); - } - return pattern; + if (wideCounters == 3) { + // Found 3 wide counters, but are they close enough in width? + // We can perform a cheap, conservative check to see if any individual + // counter is more than 1.5 times the average: + for (int i = 0; i < numCounters && wideCounters > 0; i++) { + int counter = counters[i]; + if (counters[i] > maxNarrowCounter) { + wideCounters--; + // totalWideCountersWidth = 3 * average, so this checks if counter >= 3/2 * average + if ((counter << 1) >= totalWideCountersWidth) { + throw new ReaderException("Wide bars vary too much in width, rejecting"); + } + } + } + return pattern; + } + } while (wideCounters > 3); + throw new ReaderException("Can't find 3 wide bars/spaces out of 9"); } private static char patternToChar(int pattern) throws ReaderException { @@ -189,4 +268,60 @@ public final class Code39Reader extends AbstractOneDReader { throw new ReaderException("Pattern did not match character encoding"); } -} \ No newline at end of file + private static String decodeExtended(String encoded) throws ReaderException { + int length = encoded.length(); + StringBuffer decoded = new StringBuffer(length); + for (int i = 0; i < length; i++) { + char c = encoded.charAt(i); + if (c == '+' || c == '$' || c == '%' || c == '/') { + char next = encoded.charAt(i + 1); + char decodedChar = '\0'; + switch (c) { + case '+': + // +A to +Z map to a to z + if (next >= 'A' && next <= 'Z') { + decodedChar = (char) (next + 32); + } else { + throw new ReaderException("Invalid extended code 39 sequence: " + c + next); + } + break; + case '$': + // $A to $Z map to control codes SH to SB + if (next >= 'A' && next <= 'Z') { + decodedChar = (char) (next - 64); + } else { + throw new ReaderException("Invalid extended code 39 sequence: " + c + next); + } + break; + case '%': + // %A to %E map to control codes ESC to US + if (next >= 'A' && next <= 'E') { + decodedChar = (char) (next - 38); + } else if (next >= 'F' && next <= 'W') { + decodedChar = (char) (next - 11); + } else { + throw new ReaderException("Invalid extended code 39 sequence: " + c + next); + } + break; + case '/': + // /A to /O map to ! to , and /Z maps to : + if (next >= 'A' && next <= 'O') { + decodedChar = (char) (next - 32); + } else if (next == 'Z') { + decodedChar = ':'; + } else { + throw new ReaderException("Invalid extended sequence: " + c + next); + } + break; + } + decoded.append(decodedChar); + // bump up i again since we read two characters + i++; + } else { + decoded.append(c); + } + } + return decoded.toString(); + } + +}