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Revamp the character encoding detection to use a more complicated but still crude algorithm that detects more Shift_JIS sequences correctly.

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git-svn-id: https://zxing.googlecode.com/svn/trunk@664 59b500cc-1b3d-0410-9834-0bbf25fbcc57
This commit is contained in:
srowen 2008-11-02 12:22:33 +00:00
parent 79d7b01e9e
commit 14e22bd443
3 changed files with 46 additions and 29 deletions
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52
core/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParser.java
View file

@ -254,14 +254,23 @@ final class DecodedBitStreamParser {
// that it's UTF-8.
int length = bytes.length;
boolean canBeISO88591 = true;
boolean canBeShiftJIS = true;
boolean sawDoubleByteStart = false;
int maybeSingleByteKatakanaCount = 0;
boolean lastWasPossibleDoubleByteStart = false;
for (int i = 0; i < length; i++) {
for (int i = 0; i < length && (canBeISO88591 || canBeShiftJIS); i++) {
int value = bytes[i] & 0xFF;
if (value >= 0x80 && value <= 0x9F && i < length - 1) {
if (value >= 0x7F && value <= 0x9F) {
canBeISO88591 = false;
// ISO-8859-1 shouldn't use this, but before we decide it is Shift_JIS,
// just double check that it is followed by a byte that's valid in
// the Shift_JIS encoding
}
if (value >= 0xA1 && value <= 0xDF) {
// count the number of characters that might be a Shift_JIS single-byte Katakana character
maybeSingleByteKatakanaCount++;
}
if (((value >= 0x81 && value <= 0x9F) || (value >= 0xE0 && value <= 0xEF)) && i < length - 1) {
// These start double-byte characters in Shift_JIS. Let's see if it's followed by a valid
// second byte.
sawDoubleByteStart = true;
if (lastWasPossibleDoubleByteStart) {
// If we just checked this and the last byte for being a valid double-byte
// char, don't check starting on this byte. If this and the last byte
@ -274,30 +283,27 @@ final class DecodedBitStreamParser {
lastWasPossibleDoubleByteStart = true;
int nextValue = bytes[i + 1] & 0xFF;
if (nextValue < 0x40 || nextValue > 0xFC) {
return UTF8;
canBeShiftJIS = false;
}
// There is some conflicting information out there about which bytes can follow which in
// double-byte Shift_JIS characters. The rule above seems to be the one that matches practice.
// The stricter rule below, however, is given by other resources.
/*
if ((value & 0x1) == 0) {
// if even, next value should be in [0x9F,0xFC]
// if not, we'll guess UTF-8
if (nextValue < 0x9F || nextValue > 0xFC) {
return UTF8;
}
} else {
// if odd, next value should be in [0x40,0x9E]
// if not, we'll guess UTF-8
if (nextValue < 0x40 || nextValue > 0x9E) {
return UTF8;
}
}
*/
}
}
}
return canBeISO88591 ? ISO88591 : SHIFT_JIS;
// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough. The crude heuristic is:
// - If we saw
// - at least one byte that starts a double-byte value (bytes that are rare in ISO-8859-1), or
// - over 5% of bytes that could be single-byte Katakana (also rare in ISO-8859-1),
// - and, saw no sequences that are invalid in Shift_JIS, then we conclude Shift_JIS
if ((sawDoubleByteStart || 20 * maybeSingleByteKatakanaCount > length) && canBeShiftJIS) {
return SHIFT_JIS;
}
// Otherwise, we default to ISO-8859-1 unless we know it can't be
if (canBeISO88591) {
return ISO88591;
}
// Otherwise, we take a wild guess with UTF-8
return UTF8;
}
private static int parseECIValue(BitSource bits) {

8
core/test/src/com/google/zxing/qrcode/QRCodeBlackBox2TestCase.java
View file

@ -29,10 +29,10 @@ public final class QRCodeBlackBox2TestCase extends AbstractBlackBoxTestCase {
public QRCodeBlackBox2TestCase() {
super(new File("test/data/blackbox/qrcode-2"), new MultiFormatReader(), BarcodeFormat.QR_CODE);
addTest(14, 14, 0.0f);
addTest(10, 10, 90.0f);
addTest(13, 13, 180.0f);
addTest(10, 10, 270.0f);
addTest(23, 23, 0.0f);
addTest(18, 18, 90.0f);
addTest(22, 22, 180.0f);
addTest(17, 17, 270.0f);
}
}

15
core/test/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParserTestCase.java
View file

@ -28,6 +28,17 @@ import junit.framework.TestCase;
public final class DecodedBitStreamParserTestCase extends TestCase {
public void testSimpleByteMode() throws ReaderException {
BitSourceBuilder builder = new BitSourceBuilder();
builder.write(0x04, 4); // Byte mode
builder.write(0x03, 8); // 3 bytes
builder.write(0xF1, 8);
builder.write(0xF2, 8);
builder.write(0xF3, 8);
String result = DecodedBitStreamParser.decode(builder.toByteArray(), Version.getVersionForNumber(1));
assertEquals("\u00f1\u00f2\u00f3", result);
}
public void testSimpleSJIS() throws ReaderException {
BitSourceBuilder builder = new BitSourceBuilder();
builder.write(0x04, 4); // Byte mode
builder.write(0x03, 8); // 3 bytes
@ -35,7 +46,7 @@ public final class DecodedBitStreamParserTestCase extends TestCase {
builder.write(0xA2, 8);
builder.write(0xA3, 8);
String result = DecodedBitStreamParser.decode(builder.toByteArray(), Version.getVersionForNumber(1));
assertEquals("\u00a1\u00a2\u00a3", result); // this should be "¡¢£" if your editor character encoding matches mine!
assertEquals("\uff61\uff62\uff63", result);
}
public void testECI() throws ReaderException {
@ -48,7 +59,7 @@ public final class DecodedBitStreamParserTestCase extends TestCase {
builder.write(0xA2, 8);
builder.write(0xA3, 8);
String result = DecodedBitStreamParser.decode(builder.toByteArray(), Version.getVersionForNumber(1));
assertEquals("\u00ed\u00f3\u00fa", result); // should be like "íóú"
assertEquals("\u00ed\u00f3\u00fa", result);
}
// TODO definitely need more tests here