EXIF: add support for Windows Explorer tags

README.md

@@ -146,6 +146,7 @@ About the image:
   scanned.
 - `HostComputer`: The computer and/or operating system in use at the time 
   of image creation.
+- `Keywords`: Keywords, separated by semicolons, that represent the image.
 - `Latitude`: Floating-point number indicating the latitude in degrees 
   north of the equator (e.g. 27.717).
 - `Longitude`: Floating-point number indicating the longitude in degrees 
@@ -154,6 +155,8 @@ About the image:
   without milliseconds (e.g. 2024-03-23T15:30:43). This value should be 
   updated every time the image is saved.
 - `Owner`: Name of the owner of the image.
+- `Rating`: Integer number indicating the image rating (usually between 1 
+  and 5).
 - `Software`: Name and version number of the software package(s) used to 
   create the image.
 - `Speed`: Floating-point number indicating the speed of GPS receiver 

autotests/read/jxl/gimp_exif.jxl.json

@@ -12,6 +12,14 @@
                 "key" : "ModificationDate",
                 "value" : "2025-01-05T10:18:16"
             },
+            {
+                "key" : "Keywords",
+                "value" : "kde;w11"
+            },
+            {
+                "key" : "Rating",
+                "value" : "4"
+            },
             {
                 "key" : "Software" ,
                 "value" : "GIMP 3.0.0-RC2"

autotests/read/jxr/metadata.jxr.json

@@ -59,6 +59,14 @@
             {
                 "key" : "Model",
                 "value" : "KImageFormats"
+            },
+            {
+                "key" : "Keywords",
+                "value" : "broacast;test;kde"
+            },
+            {
+                "key" : "Rating",
+                "value" : "5"
             }
         ],
         "resolution" : {

autotests/write/basic/jxl.json

@@ -37,6 +37,14 @@
             "key" : "Description",
             "value" : "テレビ放送テスト映像。(TV broadcast test image.)"
         },
+        {
+            "key" : "Keywords",
+            "value" : "kde;test"
+        },
+        {
+            "key" : "Rating",
+            "value" : "5"
+        },
         {
             "key" : "Latitude",
             "value" : "44.6478"

autotests/write/basic/jxr.json

@@ -29,6 +29,10 @@
             "key" : "Description",
             "value" : "TV broadcast test image."
         },
+        {
+            "key" : "Rating",
+            "value" : "4"
+        },
         {
             "key" : "Latitude",
             "value" : "44.6478"

src/imageformats/jxr.cpp

@@ -739,6 +739,13 @@ public:
         DESCRIPTIVEMETADATA meta;
         memset(&meta, 0, sizeof(meta));
 
+        auto ok = false;
+        auto rating = image.text(QStringLiteral(META_KEY_RATING)).toUInt(&ok);
+        if (ok) {
+            meta.pvarRatingStars.vt = DPKVT_UI2;
+            meta.pvarRatingStars.VT.uiVal = quint16(rating);
+        }
+
 #define META_CTEXT(name, field)                                                                                                                                \
     auto field = image.text(QStringLiteral(name)).toUtf8();                                                                                                    \
     if (!field.isEmpty()) {                                                                                                                                    \
@@ -1017,6 +1024,10 @@ private:
             return false;
         }
 
+        if (meta.pvarRatingStars.vt == DPKVT_UI2) {
+            m_txtMeta.insert(QStringLiteral(META_KEY_RATING), QStringLiteral("%1").arg(meta.pvarRatingStars.VT.uiVal));
+        }
+
 #define META_TEXT(name, field)                                                                                                                                 \
     if (meta.field.vt == DPKVT_LPSTR)                                                                                                                          \
         m_txtMeta.insert(QStringLiteral(name), QString::fromUtf8(meta.field.VT.pszVal));                                                                       \

src/imageformats/microexif.cpp

@@ -30,6 +30,9 @@
 #define TIFF_ARTIST 0x013B
 #define TIFF_DATETIME 0x0132
 #define TIFF_COPYRIGHT 0x8298
+#define TIFF_XPRATING 0x4746  // added by Windows Explorer Image Properties
+#define TIFF_XPTITLE 0x9C9B // added by Windows Explorer Image Properties
+#define TIFF_XPKEYWORDS 0x9C9E // added by Windows Explorer Image Properties
 
 #define TIFF_VAL_URES_NOABSOLUTE 1
 #define TIFF_VAL_URES_INCH 2
@@ -134,6 +137,9 @@ static const KnownTags staticTagTypes = {
     TagInfo(TIFF_ARTIST, ExifTagType::Utf8),
     TagInfo(TIFF_DATETIME, ExifTagType::Ascii),
     TagInfo(TIFF_COPYRIGHT, ExifTagType::Utf8),
+    TagInfo(TIFF_XPRATING, ExifTagType::Short),
+    TagInfo(TIFF_XPTITLE, ExifTagType::Byte),
+    TagInfo(TIFF_XPKEYWORDS, ExifTagType::Byte),
     TagInfo(EXIF_EXPOSURETIME, ExifTagType::Rational),
     TagInfo(EXIF_FNUMBER, ExifTagType::Rational),
     TagInfo(EXIF_EXIFIFD, ExifTagType::Long),
@@ -206,8 +212,8 @@ static const QList<std::pair<quint16, QString>> exifStrMap = {
     std::pair<quint16, QString>(EXIF_BODYSERIALNUMBER, QStringLiteral(META_KEY_SERIALNUMBER)),
     std::pair<quint16, QString>(EXIF_LENSMAKE, QStringLiteral(META_KEY_LENS_MANUFACTURER)),
     std::pair<quint16, QString>(EXIF_LENSMODEL, QStringLiteral(META_KEY_LENS_MODEL)),
-    std::pair<quint16, QString>(EXIF_LENSSERIALNUMBER, QStringLiteral(META_KEY_LENS_SERIALNUMBER)),
+    std::pair<quint16, QString>(EXIF_LENSSERIALNUMBER, QStringLiteral(META_KEY_LENS_SERIALNUMBER))
-    std::pair<quint16, QString>(EXIF_IMAGETITLE, QStringLiteral(META_KEY_TITLE)),
+    // std::pair<quint16, QString>(EXIF_IMAGETITLE, QStringLiteral(META_KEY_TITLE)) // using functions due to XP title fallback
 };
 // clang-format on
 
@@ -842,6 +848,32 @@ void MicroExif::setCopyright(const QString &s)
     setTiffString(TIFF_COPYRIGHT, s);
 }
 
+QStringList MicroExif::keywords() const
+{
+    auto val = utf16String(m_tiffTags, TIFF_XPKEYWORDS);
+    if (val.isEmpty())
+        return {};
+    return val.split(QChar(u';'), Qt::SkipEmptyParts);
+}
+
+void MicroExif::setKeywords(const QStringList &k)
+{
+    setUtf16String(m_tiffTags, TIFF_XPKEYWORDS, k.join(QChar(u';')));
+}
+
+quint16 MicroExif::rating() const
+{
+    return m_tiffTags.value(TIFF_XPRATING).toUInt();
+}
+
+void MicroExif::setRating(quint16 rating)
+{
+    if (rating == 0)
+        m_tiffTags.remove(TIFF_XPRATING);
+    else
+        m_tiffTags.insert(TIFF_XPRATING, rating);
+}
+
 QString MicroExif::make() const
 {
     return tiffString(TIFF_MAKE);
@@ -964,12 +996,18 @@ void MicroExif::setDateTimeDigitized(const QDateTime &dt)
 
 QString MicroExif::title() const
 {
-    return exifString(EXIF_IMAGETITLE);
+    auto s = exifString(EXIF_IMAGETITLE);
+    if (s.isEmpty()) { // fall back to XP title
+        s = utf16String(m_tiffTags, TIFF_XPTITLE);
+    }
+    return s;
 }
 
-void MicroExif::setImageTitle(const QString &s)
+void MicroExif::setTitle(const QString &s)
 {
     setExifString(EXIF_IMAGETITLE, s);
+    // Since there is an official title tag, I never write the non-standard Microsoft one.
+    setUtf16String(m_tiffTags, TIFF_XPTITLE, QString());
 }
 
 QUuid MicroExif::uniqueId() const
@@ -1337,6 +1375,11 @@ void MicroExif::updateImageMetadata(QImage &targetImage, bool replaceExisting) c
         if (!s.isEmpty())
             targetImage.setText(p.second, s);
     }
+    if (replaceExisting || targetImage.text(QStringLiteral(META_KEY_TITLE)).isEmpty()) {
+        auto s = title();
+        if (!s.isEmpty())
+            targetImage.setText(QStringLiteral(META_KEY_TITLE), s);
+    }
 
     // set date and time
     if (replaceExisting || targetImage.text(QStringLiteral(META_KEY_MODIFICATIONDATE)).isEmpty()) {
@@ -1423,6 +1466,18 @@ void MicroExif::updateImageMetadata(QImage &targetImage, bool replaceExisting) c
         if (v != WhiteBalance::NotSet)
             targetImage.setText(QStringLiteral(META_KEY_WHITEBALANCE), QStringLiteral("%1").arg(quint16(v)));
     }
+
+    // set Microsoft tags
+    if (replaceExisting || targetImage.text(QStringLiteral(META_KEY_KEYWORDS)).isEmpty()) {
+        auto keywords = this->keywords();
+        if (!keywords.isEmpty())
+            targetImage.setText(QStringLiteral(META_KEY_KEYWORDS), keywords.join(QChar(u';')));
+    }
+    if (replaceExisting || targetImage.text(QStringLiteral(META_KEY_RATING)).isEmpty()) {
+        auto v = rating();
+        if (v != 0)
+            targetImage.setText(QStringLiteral(META_KEY_RATING), QStringLiteral("%1").arg(quint16(v)));
+    }
 }
 
 bool MicroExif::updateImageResolution(QImage &targetImage)
@@ -1518,6 +1573,7 @@ MicroExif MicroExif::fromImage(const QImage &image)
     for (auto &&p : exifStrMap) {
         exif.setExifString(p.first, image.text(p.second));
     }
+    exif.setTitle(image.text(QStringLiteral(META_KEY_TITLE)));
 
     // TIFF Software
     if (exif.software().isEmpty()) {
@@ -1587,6 +1643,13 @@ MicroExif MicroExif::fromImage(const QImage &image)
     if (ok)
         exif.setWhiteBalance(WhiteBalance(whtb));
 
+    // Microsoft tags
+    exif.setKeywords(image.text(QStringLiteral(META_KEY_KEYWORDS)).split(QChar(u';'), Qt::SkipEmptyParts));
+
+    auto rating = image.text(QStringLiteral(META_KEY_RATING)).toUInt(&ok);
+    if (ok)
+        exif.setRating(rating);
+
     return exif;
 }
 
@@ -1676,3 +1739,29 @@ QString MicroExif::string(const Tags &tags, quint16 tagId)
 {
     return tags.value(tagId).toString();
 }
+
+void MicroExif::setUtf16String(Tags &tags, quint16 tagId, const QString &s)
+{
+    if (s.isEmpty()) {
+        tags.remove(tagId);
+        return;
+    }
+    auto s16 = s.toStdU16String();
+    QList<quint8> uba;
+    auto ba = QByteArrayView(reinterpret_cast<char*>(s16.data()), s.size() * 2);
+    for(auto&& c : ba)
+        uba.append(quint8(c));
+    uba.append(quint8('\0'));
+    uba.append(quint8('\0'));
+    tags.insert(tagId, QVariant::fromValue(uba));
+}
+
+QString MicroExif::utf16String(const Tags &tags, quint16 tagId)
+{
+    auto ba = tags.value(tagId).value<QList<quint8>>();
+    if (ba.isEmpty())
+        return {};
+    auto p16 = reinterpret_cast<char16_t*>(ba.data());
+    auto sz = std::max(ba.size() / 2 - 1, qsizetype());
+    return QString::fromUtf16(p16, sz);
+}

src/imageformats/microexif_p.h

@@ -251,6 +251,24 @@ public:
     QString copyright() const;
     void setCopyright(const QString& s);
 
+    /*!
+     * \brief keywords
+     * Keywords tag used by Windows.
+     * \note Non-standard, added by Windows Explorer.
+     * \return The list of tags.
+     */
+    QStringList keywords() const;
+    void setKeywords(const QStringList& k);
+
+    /*!
+     * \brief rating
+     * Rating tag used by Windows.
+     * \note Non-standard, added by Windows Explorer.
+     * \return The rating. Usually between 0 (not set) and 5.
+     */
+    quint16 rating() const;
+    void setRating(quint16 rating);
+
     /*!
      * \brief make
      * \return The manufacturer of the recording equipment.
@@ -319,7 +337,7 @@ public:
      * \return The title of the image.
      */
     QString title() const;
-    void setImageTitle(const QString &s);
+    void setTitle(const QString &s);
 
     /*!
      * \brief uniqueId
@@ -555,6 +573,9 @@ private:
     static void setString(Tags &tags, quint16 tagId, const QString &s);
     static QString string(const Tags &tags, quint16 tagId);
 
+    static void setUtf16String(Tags &tags, quint16 tagId, const QString &s);
+    static QString utf16String(const Tags &tags, quint16 tagId);
+
 private:
     Tags m_tiffTags;
     Tags m_exifTags;

src/imageformats/util_p.h

@@ -44,10 +44,12 @@
 #define META_KEY_DIRECTION "Direction"
 #define META_KEY_DOCUMENTNAME "DocumentName"
 #define META_KEY_HOSTCOMPUTER "HostComputer"
+#define META_KEY_KEYWORDS "Keywords"
 #define META_KEY_LATITUDE "Latitude"
 #define META_KEY_LONGITUDE "Longitude"
 #define META_KEY_MODIFICATIONDATE "ModificationDate"
 #define META_KEY_OWNER "Owner"
+#define META_KEY_RATING "Rating"
 #define META_KEY_SOFTWARE "Software"
 #define META_KEY_SPEED "Speed"
 #define META_KEY_TITLE "Title"