Handle Grayscale8 TIFFs

Correctly read and write Grayscale8 image format.

Change-Id: I537c68f94077458c69ee1de08b5b37986b54aa26
Reviewed-by: Ivan Komissarov <ABBAPOH@gmail.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

src/plugins/imageformats/tiff/qtiffhandler.cpp

@@ -245,6 +245,8 @@ bool QTiffHandlerPrivate::openForRead(QIODevice *device)
 
     if (grayscale && bitPerSample == 1 && samplesPerPixel == 1)
         format = QImage::Format_Mono;
+    else if (photometric == PHOTOMETRIC_MINISBLACK && bitPerSample == 8 && samplesPerPixel == 1)
+        format = QImage::Format_Grayscale8;
     else if ((grayscale || photometric == PHOTOMETRIC_PALETTE) && bitPerSample == 8 && samplesPerPixel == 1)
         format = QImage::Format_Indexed8;
     else if (samplesPerPixel < 4)
@@ -366,6 +368,15 @@ bool QTiffHandler::read(QImage *image)
 
                 // free redTable, greenTable and greenTable done by libtiff
             }
+        } else if (format == QImage::Format_Grayscale8) {
+            if (!image->isNull()) {
+                for (uint32 y = 0; y < height; ++y) {
+                    if (TIFFReadScanline(tiff, image->scanLine(y), y, 0) < 0) {
+                        d->close();
+                        return false;
+                    }
+                }
+            }
         } else {
             if (!image->isNull()) {
                 const int stopOnError = 1;
@@ -428,6 +439,29 @@ static bool checkGrayscale(const QVector<QRgb> &colorTable)
     return true;
 }
 
+static QVector<QRgb> effectiveColorTable(const QImage &image)
+{
+    QVector<QRgb> colors;
+    switch (image.format()) {
+    case QImage::Format_Indexed8:
+        colors = image.colorTable();
+        break;
+    case QImage::Format_Alpha8:
+        colors.resize(256);
+        for (int i = 0; i < 256; ++i)
+            colors[i] = qRgba(0, 0, 0, i);
+        break;
+    case QImage::Format_Grayscale8:
+        colors.resize(256);
+        for (int i = 0; i < 256; ++i)
+            colors[i] = qRgb(i, i, i);
+        break;
+    default:
+        Q_UNREACHABLE();
+    }
+    return colors;
+}
+
 bool QTiffHandler::write(const QImage &image)
 {
     if (!device()->isWritable())
@@ -515,12 +549,14 @@ bool QTiffHandler::write(const QImage &image)
             }
         }
         TIFFClose(tiff);
-    } else if (format == QImage::Format_Indexed8) {
-        const QVector<QRgb> colorTable = image.colorTable();
+    } else if (format == QImage::Format_Indexed8
+               || format == QImage::Format_Grayscale8
+               || format == QImage::Format_Alpha8) {
+        QVector<QRgb> colorTable = effectiveColorTable(image);
         bool isGrayscale = checkGrayscale(colorTable);
         if (isGrayscale) {
             uint16 photometric = PHOTOMETRIC_MINISBLACK;
-            if (image.colorTable().at(0) == 0xffffffff)
+            if (colorTable.at(0) == 0xffffffff)
                 photometric = PHOTOMETRIC_MINISWHITE;
             if (!TIFFSetField(tiff, TIFFTAG_PHOTOMETRIC, photometric)
                     || !TIFFSetField(tiff, TIFFTAG_COMPRESSION, compression == NoCompression ? COMPRESSION_NONE : COMPRESSION_PACKBITS)
@@ -579,7 +615,6 @@ bool QTiffHandler::write(const QImage &image)
             }
         }
         TIFFClose(tiff);
-
     } else if (!image.hasAlphaChannel()) {
         if (!TIFFSetField(tiff, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_RGB)
             || !TIFFSetField(tiff, TIFFTAG_COMPRESSION, compression == NoCompression ? COMPRESSION_NONE : COMPRESSION_LZW)

tests/auto/tiff/tst_qtiff.cpp

@@ -364,31 +364,23 @@ void tst_qtiff::readWriteNonDestructive_data()
 {
     QTest::addColumn<QImage::Format>("format");
     QTest::addColumn<QImage::Format>("expectedFormat");
-    QTest::addColumn<bool>("grayscale");
     QTest::addColumn<QImageIOHandler::Transformation>("transformation");
-    QTest::newRow("tiff mono") << QImage::Format_Mono << QImage::Format_Mono << false << QImageIOHandler::TransformationNone;
-    QTest::newRow("tiff indexed") << QImage::Format_Indexed8 << QImage::Format_Indexed8 << false << QImageIOHandler::TransformationMirror;
-    QTest::newRow("tiff argb32pm") << QImage::Format_ARGB32_Premultiplied << QImage::Format_ARGB32_Premultiplied << false << QImageIOHandler::TransformationRotate90;
-    QTest::newRow("tiff rgb32") << QImage::Format_RGB32 << QImage::Format_RGB32 << false << QImageIOHandler::TransformationRotate270;
-    QTest::newRow("tiff grayscale") << QImage::Format_Indexed8 << QImage::Format_Indexed8 << true << QImageIOHandler::TransformationFlip;
+    QTest::newRow("tiff mono") << QImage::Format_Mono << QImage::Format_Mono << QImageIOHandler::TransformationNone;
+    QTest::newRow("tiff indexed") << QImage::Format_Indexed8 << QImage::Format_Indexed8 << QImageIOHandler::TransformationMirror;
+    QTest::newRow("tiff argb32pm") << QImage::Format_ARGB32_Premultiplied << QImage::Format_ARGB32_Premultiplied << QImageIOHandler::TransformationRotate90;
+    QTest::newRow("tiff rgb32") << QImage::Format_RGB32 << QImage::Format_RGB32 << QImageIOHandler::TransformationRotate270;
+    QTest::newRow("tiff grayscale") << QImage::Format_Grayscale8 << QImage::Format_Grayscale8 << QImageIOHandler::TransformationFlip;
 }
 
 void tst_qtiff::readWriteNonDestructive()
 {
     QFETCH(QImage::Format, format);
     QFETCH(QImage::Format, expectedFormat);
-    QFETCH(bool, grayscale);
     QFETCH(QImageIOHandler::Transformation, transformation);
+
     QImage image = QImage(prefix + "colorful.bmp").convertToFormat(format);
     QVERIFY(!image.isNull());
 
-    if (grayscale) {
-        QVector<QRgb> colors;
-        for (int i = 0; i < 256; ++i)
-            colors << qRgb(i, i, i);
-        image.setColorTable(colors);
-    }
-
     QByteArray output;
     QBuffer buf(&output);
     QVERIFY(buf.open(QIODevice::WriteOnly));