Index: src/hiderectitem.h
===================================================================
--- src/hiderectitem.h
+++ src/hiderectitem.h
@@ -37,6 +37,15 @@
 {
 public:
     HideRectItem();
+
+    QRectF rect() const;
+    void setRect(const QRectF &rect);
+
+    qreal devicePixelRatio() const;
+    void setDevicePixelRatio(qreal dpr);
+
+private:
+    qreal m_devicePixelRatio;
 };
 
 }  // NameSpace KSaneIface
Index: src/hiderectitem.cpp
===================================================================
--- src/hiderectitem.cpp
+++ src/hiderectitem.cpp
@@ -33,10 +33,32 @@
 {
 
 HideRectItem::HideRectItem()
+    : m_devicePixelRatio(1.0)
 {
     setOpacity(0.4);
     setPen(Qt::NoPen);
     setBrush(Qt::black);
 }
 
+QRectF HideRectItem::rect() const
+{
+    QRectF r = QGraphicsRectItem::rect();
+    return QRectF(r.topLeft() * m_devicePixelRatio, r.size() * m_devicePixelRatio);
+}
+
+void HideRectItem::setRect(const QRectF &rect)
+{
+    QGraphicsRectItem::setRect(QRectF(rect.topLeft() / m_devicePixelRatio, rect.size() / m_devicePixelRatio));
+}
+
+qreal HideRectItem::devicePixelRatio() const
+{
+    return m_devicePixelRatio;
+}
+
+void HideRectItem::setDevicePixelRatio(qreal dpr)
+{
+    m_devicePixelRatio = dpr;
+}
+
 }  // NameSpace KSaneIface
Index: src/ksaneviewer.h
===================================================================
--- src/ksaneviewer.h
+++ src/ksaneviewer.h
@@ -115,6 +115,8 @@
     int  refineRow(int fromRow, int toRow, int rowStart, int rowEnd);
     int  refineColumn(int fromCol, int toCol, int colStart, int colEnd);
 
+    QPointF scenePos(QMouseEvent *e) const;
+
     struct Private;
     Private *const d;
 
Index: src/ksaneviewer.cpp
===================================================================
--- src/ksaneviewer.cpp
+++ src/ksaneviewer.cpp
@@ -85,7 +85,8 @@
 
     // Init the scene
     d->scene = new QGraphicsScene(this);
-    d->scene->setSceneRect(0, 0, img->width(), img->height());
+    const auto dpr = img->devicePixelRatio();
+    d->scene->setSceneRect(0, 0, img->width() / dpr, img->height() / dpr);
     setScene(d->scene);
 
     d->selection = new SelectionItem(QRectF());
@@ -141,7 +142,10 @@
 void KSaneViewer::drawBackground(QPainter *painter, const QRectF &rect)
 {
     painter->fillRect(rect, QColor(0x70, 0x70, 0x70));
-    painter->drawImage(rect, *d->img, rect);
+    QRectF r = rect & sceneRect();
+    const qreal dpr = d->img->devicePixelRatio();
+    QRectF srcRect = QRectF(r.topLeft() * dpr, r.size() * dpr);
+    painter->drawImage(r, *d->img, srcRect);
 }
 
 // ------------------------------------------------------------------------
@@ -166,9 +170,18 @@
     // clear zoom
     setMatrix(QMatrix());
 
-    d->scene->setSceneRect(0, 0, img->width(), img->height());
+    const auto dpr = img->devicePixelRatio();
+    d->scene->setSceneRect(0, 0, img->width() / dpr, img->height() / dpr);
     d->selection->setMaxRight(img->width());
     d->selection->setMaxBottom(img->height());
+
+    d->selection->setDevicePixelRatio(dpr);
+    d->hideTop->setDevicePixelRatio(dpr);
+    d->hideBottom->setDevicePixelRatio(dpr);
+    d->hideRight->setDevicePixelRatio(dpr);
+    d->hideLeft->setDevicePixelRatio(dpr);
+    d->hideArea->setDevicePixelRatio(dpr);
+
     d->img = img;
 }
 
@@ -527,7 +540,7 @@
     if (e->button() == Qt::LeftButton) {
         d->m_left_last_x = e->x();
         d->m_left_last_y = e->y();
-        QPointF scenePoint = mapToScene(e->pos());
+        QPointF scenePoint = scenePos(e) * d->selection->devicePixelRatio();
         d->lastSPoint = scenePoint;
         if (e->modifiers() != Qt::ControlModifier) {
             if (!d->selection->isVisible()) {
@@ -556,7 +569,7 @@
             clearActiveSelection();
         }
 
-        QPointF scenePoint = mapToScene(e->pos());
+        QPointF scenePoint = scenePos(e) * d->selection->devicePixelRatio();
         for (int i = 0; i < d->selectionList.size(); i++) {
             if (d->selectionList[i]->intersects(scenePoint) == SelectionItem::AddRemove) {
                 d->scene->removeItem(d->selectionList[i]);
@@ -573,6 +586,7 @@
         if (!removed && (d->selection->intersects(scenePoint) == SelectionItem::AddRemove)) {
             // add the current selection
             SelectionItem *tmp = new SelectionItem(d->selection->rect());
+            tmp->setDevicePixelRatio(d->img->devicePixelRatio());
             d->selectionList.push_back(tmp);
             d->selectionList.back()->setSaved(true);
             d->selectionList.back()->saveZoom(transform().m11());
@@ -604,7 +618,7 @@
 // ------------------------------------------------------------------------
 void KSaneViewer::mouseMoveEvent(QMouseEvent *e)
 {
-    QPointF scenePoint = mapToScene(e->pos());
+    QPointF scenePoint = scenePos(e) * d->selection->devicePixelRatio();
 
     if (e->buttons()&Qt::LeftButton) {
         if (e->modifiers() == Qt::ControlModifier) {
@@ -913,6 +927,7 @@
                                 float selArea = (float)(wSelEnd - wSelStart) * (float)(hSelEnd - hSelStart);
                                 if (selArea > (area * MIN_AREA_SIZE)) {
                                     SelectionItem *tmp = new SelectionItem(QRect(QPoint(x1, y1), QPoint(x2, y2)));
+                                    tmp->setDevicePixelRatio(d->img->devicePixelRatio());
                                     d->selectionList.push_back(tmp);
                                     d->selectionList.back()->setSaved(true);
                                     d->selectionList.back()->saveZoom(transform().m11());
@@ -1142,4 +1157,16 @@
     return col;
 }
 
+QPointF KSaneViewer::scenePos(QMouseEvent *e) const
+{
+    // QGraphicsView::mapToScene() maps only QPoints, but in highdpi mode we want
+    // to deal with non-rounded coordinates, that's why QPainterPath wrapper is used.
+    // QMouseEvent::localPos() currently returns a rounded QPointF
+    // (https://codereview.qt-project.org/259785), so we have to extract a fractional
+    // part from QMouseEvent::screenPos().
+    const QPointF screenPos = e->screenPos();
+    QPointF delta = screenPos - screenPos.toPoint();
+    return mapToScene(QPainterPath(e->pos() + delta)).currentPosition();
+}
+
 }  // NameSpace KSaneIface
Index: src/ksanewidget_p.cpp
===================================================================
--- src/ksanewidget_p.cpp
+++ src/ksanewidget_p.cpp
@@ -715,7 +715,9 @@
         x = (int)(SCALED_PREVIEW_MAX_SIDE / ratio);
     }
 
-    m_previewImg = QImage(x, y, QImage::Format_RGB32);
+    const qreal dpr = q->devicePixelRatioF();
+    m_previewImg = QImage(QSize(x, y) * dpr, QImage::Format_RGB32);
+    m_previewImg.setDevicePixelRatio(dpr);
     m_previewImg.fill(0xFFFFFFFF);
 
     // set the new image
Index: src/selectionitem.h
===================================================================
--- src/selectionitem.h
+++ src/selectionitem.h
@@ -65,6 +65,9 @@
     QPointF fixTranslation( QPointF dp);
     QRectF rect();
 
+    qreal devicePixelRatio() const;
+    void setDevicePixelRatio(qreal dpr);
+
 public:
     // Graphics Item methods
     QRectF boundingRect() const override;
Index: src/selectionitem.cpp
===================================================================
--- src/selectionitem.cpp
+++ src/selectionitem.cpp
@@ -54,6 +54,7 @@
     qreal      invZoom;
     qreal      selMargin;
     QRectF     addRemRect;
+    qreal      devicePixelRatio;
 };
 
 SelectionItem::SelectionItem(const QRectF &rect) : QGraphicsItem(), d(new Private)
@@ -65,8 +66,10 @@
 
     d->penDark.setColor(Qt::black);
     d->penDark.setStyle(Qt::SolidLine);
+    d->penDark.setWidth(0);
     d->penLight.setColor(Qt::white);
     d->penLight.setStyle(Qt::DashLine);
+    d->penLight.setWidth(0);
 
     // FIXME We should probably use some standard KDE color here and not hard code it
     d->penAddRemFg.setColor(Qt::darkGreen);
@@ -79,6 +82,8 @@
     d->selMargin = selMargin;
 
     d->addRemRect = QRectF(0, 0, 0, 0);
+
+    d->devicePixelRatio = 1.0;
 }
 
 SelectionItem::~SelectionItem()
@@ -97,7 +102,7 @@
 
     qreal margin = addRemMargin * d->invZoom;
     QPointF pMargin = addRemMarginPoint * d->invZoom;
-    d->addRemRect = QRectF(d->rect.center() - pMargin, QSizeF(margin * 2.0, margin * 2.0));
+    d->addRemRect = QRectF(d->rect.center() / d->devicePixelRatio - pMargin, QSizeF(margin * 2.0, margin * 2.0));
     d->penAddRemFg.setWidthF(3.0 * d->invZoom);
 }
 
@@ -193,10 +198,7 @@
         update();
     }
 
-    if ((point.x() > d->addRemRect.left()) &&
-            (point.x() < d->addRemRect.right()) &&
-            (point.y() > d->addRemRect.top()) &&
-            (point.y() < d->addRemRect.bottom())) {
+    if (d->addRemRect.contains(point / d->devicePixelRatio)) {
         return AddRemove;
     }
     return Move;
@@ -225,7 +227,7 @@
     // calculate the add/remove rectangle
     qreal margin = addRemMargin * d->invZoom;
     QPointF pMargin = addRemMarginPoint * d->invZoom;
-    d->addRemRect = QRectF(d->rect.center() - pMargin, QSizeF(margin * 2, margin * 2));
+    d->addRemRect = QRectF(d->rect.center() / d->devicePixelRatio - pMargin, QSizeF(margin * 2, margin * 2));
 }
 
 QPointF SelectionItem::fixTranslation(QPointF dp)
@@ -250,46 +252,45 @@
     return d->rect;
 }
 
-QRectF SelectionItem::boundingRect() const
+qreal SelectionItem::devicePixelRatio() const
 {
-    QRectF tmp(d->rect.topLeft() - boundMargin, d->rect.bottomRight() + boundMargin);
-    if (tmp.top() > d->addRemRect.top()) {
-        tmp.setTop(d->addRemRect.top());
-    }
-    if (tmp.left() > d->addRemRect.left()) {
-        tmp.setLeft(d->addRemRect.left());
-    }
-
-    if (tmp.bottom() < d->addRemRect.bottom()) {
-        tmp.setBottom(d->addRemRect.bottom());
-    }
+    return d->devicePixelRatio;
+}
 
-    if (tmp.right() < d->addRemRect.right()) {
-        tmp.setRight(d->addRemRect.right());
-    }
+void SelectionItem::setDevicePixelRatio(qreal dpr)
+{
+    d->devicePixelRatio = dpr;
+}
 
-    return tmp;
+QRectF SelectionItem::boundingRect() const
+{
+    const auto dpr = d->devicePixelRatio;
+    QRectF tmp(d->rect.topLeft() / dpr - boundMargin, d->rect.bottomRight() / dpr + boundMargin);
+    return tmp.united(d->addRemRect);
 }
 
 void SelectionItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
 {
+    const auto dpr = d->devicePixelRatio;
+    QRectF rect(d->rect.topLeft() / dpr, d->rect.size() / dpr);
+
     painter->setPen(d->penDark);
-    painter->drawRect(d->rect);
+    painter->drawRect(rect);
 
     painter->setPen(d->penLight);
-    painter->drawRect(d->rect);
+    painter->drawRect(rect);
 
     if (d->showAddRem) {
         painter->fillRect(d->addRemRect, QBrush(Qt::white));
-        QLineF minus(d->addRemRect.left() + 3 * d->invZoom, d->rect.center().y(),
-                     d->addRemRect.right() - 3 * d->invZoom, d->rect.center().y());
+        QLineF minus(d->addRemRect.left() + 3 * d->invZoom, d->addRemRect.center().y(),
+                     d->addRemRect.right() - 3 * d->invZoom, d->addRemRect.center().y());
         painter->setPen(d->penAddRemFg);
 
         painter->drawLine(minus);
 
         if (!d->isSaved) {
-            QLineF plus(d->rect.center().x(), d->addRemRect.top() + 3 * d->invZoom,
-                        d->rect.center().x(), d->addRemRect.bottom() - 3 * d->invZoom);
+            QLineF plus(d->addRemRect.center().x(), d->addRemRect.top() + 3 * d->invZoom,
+                        d->addRemRect.center().x(), d->addRemRect.bottom() - 3 * d->invZoom);
             painter->drawLine(plus);
         }
     }