Fix smooth scaling of Format_Mono and Format_MonoLSB

Fixes: QTBUG-117713
Pick-to: 6.6 6.5 6.2
Change-Id: I2fb071a4d2229da50dfacb0a92c51c3e4ea57a74
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 14 insertions, 4 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index d913dfa2ec..2770a04bce 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -4862,14 +4862,24 @@ QImage Q_TRACE_INSTRUMENT(qtgui) QImage::transformed(const QTransform &matrix, Q
             || (ws * hs) >= (1<<20)
 #endif
             ) {
+            QImage scaledImage;
             if (mat.m11() < 0.0F && mat.m22() < 0.0F) { // horizontal/vertical flip
-                return smoothScaled(wd, hd).mirrored(true, true).convertToFormat(format());
+                scaledImage = smoothScaled(wd, hd).mirrored(true, true);
             } else if (mat.m11() < 0.0F) { // horizontal flip
-                return smoothScaled(wd, hd).mirrored(true, false).convertToFormat(format());
+                scaledImage = smoothScaled(wd, hd).mirrored(true, false);
             } else if (mat.m22() < 0.0F) { // vertical flip
-                return smoothScaled(wd, hd).mirrored(false, true).convertToFormat(format());
+                scaledImage = smoothScaled(wd, hd).mirrored(false, true);
             } else { // no flipping
-                return smoothScaled(wd, hd).convertToFormat(format());
+                scaledImage = smoothScaled(wd, hd);
+            }
+
+            switch (format()) {
+            case QImage::Format_Mono:
+            case QImage::Format_MonoLSB:
+            case QImage::Format_Indexed8:
+                return scaledImage;
+            default:
+                return scaledImage.convertToFormat(format());
             }
         }
     }