Merge pull request opencv#24350 from dkurt:py_return_non_utf8_string

Encode QR code data to UTF-8 opencv#24350

### Pull Request Readiness Checklist

**Merge with extra**: opencv/opencv_extra#1105

resolves opencv#23728

This is first PR in a series. Here we just return a raw Unicode. Later I will try expand QR codes decoding methods to use ECI assignment number and return a string with proper encoding, not only UTF-8 or raw unicode.

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/objdetect/src/qrcode.cpp

@@ -2727,6 +2727,58 @@ bool QRDecode::samplingForVersion()
     return true;
 }
 
+
+static bool checkASCIIcompatible(const uint8_t* str, const size_t size) {
+    for (size_t i = 0; i < size; ++i) {
+        uint8_t byte = str[i];
+        if (byte >= 0x80)
+            return false;
+    }
+    return true;
+}
+
+static bool checkUTF8(const uint8_t* str, const size_t size) {
+    for (size_t i = 0; i < size; ++i) {
+        uint8_t byte = str[i];
+        if (byte >= 0x80) {
+            // Check that symbol is encoded correctly.
+
+            // Count number of bytes per symbol as a number of leading non-zero bits
+            uint8_t numBytesPerSymbol;
+            if ((byte & 0xe0) == 0xc0)
+                numBytesPerSymbol = 2;
+            else if ((byte & 0xf0) == 0xe0)
+                numBytesPerSymbol = 3;
+            else if ((byte & 0xf8) == 0xf0)
+                numBytesPerSymbol = 4;
+            else
+                return false;
+
+            for (size_t j = 1; j < numBytesPerSymbol; ++j) {
+                if (i + j >= size || (str[i + j] & 0xc0) != 0x80) {
+                    return false;
+                }
+            }
+            i += numBytesPerSymbol - 1;
+        }
+    }
+    return true;
+}
+
+static std::string encodeUTF8_bytesarray(const uint8_t* str, const size_t size) {
+    std::ostringstream res;
+    for (size_t i = 0; i < size; ++i) {
+        uint8_t byte = str[i];
+        if (byte >= 0x80) {
+            res << (char)(0xc0 | (byte >> 6));
+            res << (char)(0x80 | (byte & 0x3f));
+        } else {
+            res << (char)byte;
+        }
+    }
+    return res.str();
+}
+
 bool QRDecode::decodingProcess()
 {
 #ifdef HAVE_QUIRC
@@ -2756,11 +2808,58 @@ bool QRDecode::decodingProcess()
 
     if (errorCode != 0) { return false; }
 
-    for (int i = 0; i < qr_code_data.payload_len; i++)
+    CV_LOG_INFO(NULL, "QR: decoded with .version=" << qr_code_data.version << " .data_type=" << qr_code_data.data_type << " .eci=" << qr_code_data.eci << " .payload_len=" << qr_code_data.payload_len)
+
+    switch (qr_code_data.data_type)
     {
-        result_info += qr_code_data.payload[i];
+        case QUIRC_DATA_TYPE_NUMERIC:
+            if (!checkASCIIcompatible(qr_code_data.payload, qr_code_data.payload_len)) {
+                CV_LOG_INFO(NULL, "QR: DATA_TYPE_NUMERIC payload must be ACSII compatible string");
+                return false;
+            }
+            result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+            return true;
+        case QUIRC_DATA_TYPE_ALPHA:
+            if (!checkASCIIcompatible(qr_code_data.payload, qr_code_data.payload_len)) {
+                CV_LOG_INFO(NULL, "QR: DATA_TYPE_ALPHA payload must be ASCII compatible string");
+                return false;
+            }
+            result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+            return true;
+        case QUIRC_DATA_TYPE_BYTE:
+            // https://en.wikipedia.org/wiki/Extended_Channel_Interpretation
+            if (qr_code_data.eci == QUIRC_ECI_UTF_8) {
+                CV_LOG_INFO(NULL, "QR: payload ECI is UTF-8");
+                if (!checkUTF8(qr_code_data.payload, qr_code_data.payload_len)) {
+                    CV_LOG_INFO(NULL, "QUIRC_DATA_TYPE_BYTE with UTF-8 ECI must be UTF-8 compatible string");
+                    return false;
+                }
+                result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+            } else if (qr_code_data.eci == 25/*ECI_UTF_16BE*/) {
+                CV_LOG_INFO(NULL, "QR: UTF-16BE ECI is not supported");
+                return false;
+            } else if (checkASCIIcompatible(qr_code_data.payload, qr_code_data.payload_len)) {
+                CV_LOG_INFO(NULL, "QR: payload is ASCII compatible (special handling for symbols encoding is not needed)");
+                result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+            } else {
+                if (checkUTF8(qr_code_data.payload, qr_code_data.payload_len)) {
+                    CV_LOG_INFO(NULL, "QR: payload QUIRC_DATA_TYPE_BYTE is UTF-8 compatible, return as-is");
+                    result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+                } else {
+                    CV_LOG_INFO(NULL, "QR: assume 1-byte per symbol encoding");
+                    result_info = encodeUTF8_bytesarray(qr_code_data.payload, qr_code_data.payload_len);
+                }
+            }
+            return true;
+        case QUIRC_DATA_TYPE_KANJI:
+            // FIXIT BUG: we must return UTF-8 compatible string
+            CV_LOG_WARNING(NULL, "QR: Kanji is not supported properly");
+            result_info.assign((const char*)qr_code_data.payload, qr_code_data.payload_len);
+            return true;
     }
-    return true;
+
+    CV_LOG_WARNING(NULL, "QR: unsupported QR data type");
+    return false;
 #else
     return false;
 #endif

modules/objdetect/test/test_qrcode.cpp

@@ -637,4 +637,25 @@ TEST_P(Objdetect_QRCode_detectAndDecodeMulti, decode_9_qrcodes_version7)
 
 #endif // UPDATE_QRCODE_TEST_DATA
 
+TEST(Objdetect_QRCode_detectAndDecode, utf8_output)
+{
+#ifndef HAVE_QUIRC
+    throw SkipTestException("Quirc is required for decoding");
+#else
+    const std::string name_current_image = "umlaut.png";
+    const std::string root = "qrcode/";
+
+    std::string image_path = findDataFile(root + name_current_image);
+    Mat src = imread(image_path);
+    ASSERT_FALSE(src.empty()) << "Can't read image: " << image_path;
+
+    QRCodeDetector qrcode;
+    std::vector<Point> corners;
+    Mat straight;
+    std::string decoded_info = qrcode.detectAndDecode(src, corners, straight);
+    EXPECT_FALSE(decoded_info.empty());
+    EXPECT_NE(decoded_info.find("M\xc3\xbcllheimstrasse"), std::string::npos);
+#endif // HAVE_QUIRC
+}
+
 }} // namespace