diff --git a/viewer/image_viewer/JFJochAzIntImage.cpp b/viewer/image_viewer/JFJochAzIntImage.cpp
index a9905f24..7ccf3ce4 100644
--- a/viewer/image_viewer/JFJochAzIntImage.cpp
+++ b/viewer/image_viewer/JFJochAzIntImage.cpp
@@ -23,7 +23,6 @@ void JFJochAzIntImage::Clear() {
 void JFJochAzIntImage::imageLoaded(std::shared_ptr<const JFJochReaderImage> in_image) {
     if (!in_image) {
         Clear();
-        CalcROI();
         return;
     }
 
@@ -71,7 +70,6 @@ void JFJochAzIntImage::imageLoaded(std::shared_ptr<const JFJochReaderImage> in_i
         // Render the image and redraw using base class functionality
         RenderImage();
         Redraw();
-        CalcROI();
     } else {
         Clear();
     }
diff --git a/viewer/image_viewer/JFJochDiffractionImage.cpp b/viewer/image_viewer/JFJochDiffractionImage.cpp
index 7c12ab74..45b6d56e 100644
--- a/viewer/image_viewer/JFJochDiffractionImage.cpp
+++ b/viewer/image_viewer/JFJochDiffractionImage.cpp
@@ -127,7 +127,6 @@ void JFJochDiffractionImage::LoadImageInternal() {
     W = image->Dataset().experiment.GetXPixelsNum();
     H = image->Dataset().experiment.GetYPixelsNum();
 
-    pixel_values_valid_ = false;   // image_fp is filled on demand, see EnsurePixelValues
 }
 
 void JFJochDiffractionImage::ColorRow(size_t y, const PixelColorMap &map, QRgb *out) const {
@@ -150,34 +149,6 @@ void JFJochDiffractionImage::ColorRow(size_t y, const PixelColorMap &map, QRgb *
     }
 }
 
-void JFJochDiffractionImage::EnsurePixelValues() {
-    if (pixel_values_valid_ || !image)
-        return;
-
-    const auto &img = image->Image();
-    image_fp.resize(W*H);
-
-    QVector<int> rows;
-    rows.reserve(H);
-    for (int y = 0; y < H; ++y) rows.push_back(y);
-
-    // Fill the float image with pixel data from the array
-    QtConcurrent::blockingMap(rows, [&](int y) {
-        for (size_t pxl = y * W; pxl < (y + 1) * W; pxl++) {
-            auto val = img[pxl];
-            if (val == GAP_PXL_VALUE)
-                image_fp[pxl] = NAN;
-            else if (val == ERROR_PXL_VALUE)
-                image_fp[pxl] = -INFINITY;
-            else if (val == SATURATED_PXL_VALUE)
-                image_fp[pxl] = INFINITY;
-            else
-                image_fp[pxl] = static_cast<float>(val);
-        }
-    });
-
-    pixel_values_valid_ = true;
-}
 
 void JFJochDiffractionImage::DrawSpots() {
     // Compute current visible area in scene coordinates
@@ -1011,6 +982,89 @@ QString JFJochDiffractionImage::HoverResolutionLabel() const {
     return QString("d = %1 \u00C5").arg(QString::number(hover_resolution, 'f', 2));
 }
 
+ROIMessage JFJochDiffractionImage::AccumulateROI(
+    int64_t xmin, int64_t xmax, int64_t ymin, int64_t ymax,
+    const std::function<bool(int64_t, int64_t)> &inside) const {
+    int64_t roi_val = 0;
+    uint64_t roi_val_2 = 0;
+    int64_t roi_max = INT64_MIN;
+    uint64_t roi_npixel = 0;
+    uint64_t roi_npixel_masked = 0;
+    float x_weighted = 0.0f;
+    float y_weighted = 0.0f;
+
+    // Clamp bounds defensively to the image
+    xmin = std::max<int64_t>(0, xmin);
+    ymin = std::max<int64_t>(0, ymin);
+    xmax = std::min<int64_t>(W, xmax);
+    ymax = std::min<int64_t>(H, ymax);
+
+    const auto &pixels = image->Image();
+
+    for (int64_t y = ymin; y < ymax; ++y) {
+        for (int64_t x = xmin; x < xmax; ++x) {
+            if (!inside(x, y)) continue;
+
+            const int32_t val = pixels[x + W * y];
+
+            if (val == SATURATED_PXL_VALUE || val == ERROR_PXL_VALUE) {
+                roi_npixel_masked++;
+            } else if (val != GAP_PXL_VALUE) {
+                x_weighted += static_cast<float>(val) * x;
+                y_weighted += static_cast<float>(val) * y;
+                roi_val += val;
+                roi_val_2 += static_cast<uint64_t>(val) * val;
+                if (val > roi_max) roi_max = val;
+                roi_npixel++;
+            }
+        }
+    }
+
+    return ROIMessage{
+        .sum = roi_val,
+        .sum_square = roi_val_2,
+        .max_count = roi_max,
+        .pixels = roi_npixel,
+        .pixels_masked = roi_npixel_masked,
+        .x_weighted = std::lroundf(x_weighted),
+        .y_weighted = std::lroundf(y_weighted),
+    };
+}
+
+void JFJochDiffractionImage::CalcROI() {
+    if (!image || W * H == 0) {
+        auto msg = ROIMessage{.pixels = 0, .pixels_masked = 0};
+        emit roiCalculated(msg);
+        return;
+    }
+
+    auto box_norm = roiBox.normalized();
+
+    // Using the rectangle as-is; you can adjust inclusivity if needed
+    const int64_t xmin = box_norm.left();
+    const int64_t xmax = box_norm.right();
+    const int64_t ymin = box_norm.top();
+    const int64_t ymax = box_norm.bottom();
+
+    ROIMessage msg{};
+    if (roi_type == RoiType::RoiBox)
+        msg = AccumulateROI(xmin, xmax, ymin, ymax,
+                            [](int64_t, int64_t) { return true; });   // everything in the rectangle
+    else {
+        const QPointF delta = roiStartPos - roiEndPos;
+        const float cx = static_cast<float>(roiStartPos.x());
+        const float cy = static_cast<float>(roiStartPos.y());
+        const float r2 = static_cast<float>(delta.x() * delta.x() + delta.y() * delta.y());
+        msg = AccumulateROI(xmin, xmax, ymin, ymax,
+                            [cx, cy, r2](int64_t x, int64_t y) {
+                                const float dx = static_cast<float>(x) - cx;
+                                const float dy = static_cast<float>(y) - cy;
+                                return dx * dx + dy * dy <= r2;
+                            });
+    }
+    emit roiCalculated(msg);
+}
+
 QString JFJochDiffractionImage::PixelLabel(int x, int y) const {
     if (!image)
         return {};
diff --git a/viewer/image_viewer/JFJochDiffractionImage.h b/viewer/image_viewer/JFJochDiffractionImage.h
index 3ba3884e..4d717001 100644
--- a/viewer/image_viewer/JFJochDiffractionImage.h
+++ b/viewer/image_viewer/JFJochDiffractionImage.h
@@ -3,6 +3,8 @@
 
 #pragma once
 
+#include <functional>
+
 #include <QPainterPath>
 
 #include "JFJochImage.h"
@@ -29,6 +31,12 @@ Q_OBJECT
     // Counts are exact integers: label them from the int32 image rather than from a float copy,
     // which both avoids materialising that copy and cannot round large summed values.
     [[nodiscard]] QString PixelLabel(int x, int y) const override;
+
+    // This is the view that has detector counts, so it is the one that offers an ROI
+    [[nodiscard]] bool AllowROI() const override { return true; }
+    void CalcROI() override;
+    [[nodiscard]] ROIMessage AccumulateROI(int64_t xmin, int64_t xmax, int64_t ymin, int64_t ymax,
+                                           const std::function<bool(int64_t, int64_t)> &inside) const;
     void drawForeground(QPainter *painter, const QRectF &rect) override;
 public:
     enum class RingMode {Auto, Estimation, Manual, None, IceRings};
@@ -39,11 +47,9 @@ private:
 
     void addCustomOverlay() override;
     void LoadImageInternal();
-    // Colour straight from the int32 detector image; image_fp is only materialised when the
-    // base class actually needs pixel values (ROI statistics, per-pixel labels).
+    // Colour straight from the int32 detector image; no float copy of it is ever built
     void ColorRow(size_t y, const PixelColorMap &map, QRgb *out) const override;
-    void EnsurePixelValues() override;
-    bool pixel_values_valid_ = false;
+
     void DrawResolutionRings();
     void DrawROIs();
     void DrawAzimuthalROI(const ROIAzimuthal &az, const QColor &color, const DiffractionGeometry &geom);
@@ -113,6 +119,7 @@ private:
     void mouseHover(const QPointF &scenePos, Qt::KeyboardModifiers modifiers) override;
 
 signals:
+    void roiCalculated(ROIMessage &output);
     void roiGeometryEdited(ROIDefinition rois);
     void roiSelected(QString name);   // user picked an ROI by clicking it on the image
 public slots:
diff --git a/viewer/image_viewer/JFJochGridScanImage.cpp b/viewer/image_viewer/JFJochGridScanImage.cpp
index 7bb761fd..c4bfc1bd 100644
--- a/viewer/image_viewer/JFJochGridScanImage.cpp
+++ b/viewer/image_viewer/JFJochGridScanImage.cpp
@@ -14,7 +14,6 @@ void JFJochGridScanImage::clear() {
     if (scene())
         scene()->clear();
     resetScenePointers();
-    CalcROI();
 }
 
 void JFJochGridScanImage::loadData(const std::vector<float> &data, const GridScanSettings &settings, bool in_one_over_d2) {
@@ -60,7 +59,6 @@ void JFJochGridScanImage::loadData(const std::vector<float> &data, const GridSca
 
     RenderImage();
     Redraw();
-    CalcROI();
 }
 
 void JFJochGridScanImage::mouseHover(const QPointF &pt, Qt::KeyboardModifiers modifiers) {
diff --git a/viewer/image_viewer/JFJochImage.cpp b/viewer/image_viewer/JFJochImage.cpp
index 3ed3b9ed..47dc7a04 100644
--- a/viewer/image_viewer/JFJochImage.cpp
+++ b/viewer/image_viewer/JFJochImage.cpp
@@ -238,18 +238,20 @@ void JFJochImage::mousePressEvent(QMouseEvent *event) {
             return;
         }
 
-        active_handle_ = hitTestROIHandle(scenePos, 4.0 / std::sqrt(std::max(1e-4, scale_factor)));
+        active_handle_ = AllowROI()
+                         ? hitTestROIHandle(scenePos, 4.0 / std::sqrt(std::max(1e-4, scale_factor)))
+                         : ResizeHandle::None;
 
         if (active_handle_ != ResizeHandle::None && active_handle_ != ResizeHandle::Inside) {
             mouse_event_type = MouseEventType::ResizingROI;
             roiStartPos = roiBox.topLeft();
             roiEndPos = roiBox.bottomRight();
             setCursor(Qt::SizeAllCursor);
-        } else if (roiBox.contains(scenePos)) {
+        } else if (AllowROI() && roiBox.contains(scenePos)) {
             mouse_event_type = MouseEventType::MovingROI;
             lastMousePos = event->pos();
             setCursor(Qt::ClosedHandCursor);
-        } else if (event->modifiers() & Qt::Modifier::SHIFT) {
+        } else if (AllowROI() && (event->modifiers() & Qt::Modifier::SHIFT)) {
             mouse_event_type = MouseEventType::DrawingROI;
             roiStartPos = RoundPoint(scenePos);
             roiEndPos = roiStartPos;
@@ -333,6 +335,8 @@ void JFJochImage::mouseMoveEvent(QMouseEvent *event) {
             break;
         }
         case MouseEventType::None: {
+            if (!AllowROI())
+                break;
             const qreal tol = 4.0 / std::sqrt(std::max(1e-4, scale_factor));
             ResizeHandle h = hitTestROIHandle(scenePos, tol);
             // Update hover state so overlay can draw arrows/handles accordingly
@@ -400,7 +404,7 @@ void JFJochImage::contextMenuEvent(QContextMenuEvent *event) {
     QAction *saveWithOverlayAct = menu.addAction(tr("Save image with overlay as JPEG..."));
     menu.addSeparator();
     QAction *fitAct = menu.addAction(tr("Fit image to view"));
-    QAction *clearRoiAct = menu.addAction(tr("Clear ROI"));
+    QAction *clearRoiAct = AllowROI() ? menu.addAction(tr("Clear ROI")) : nullptr;
 
     const bool hasImage = (W > 0 && H > 0 && !frame_->isNull());
     copyImageAct->setEnabled(hasImage);
@@ -421,7 +425,7 @@ void JFJochImage::contextMenuEvent(QContextMenuEvent *event) {
         saveImageToFile(true);
     } else if (chosen == fitAct) {
         fitToView();
-    } else if (chosen == clearRoiAct) {
+    } else if (clearRoiAct && chosen == clearRoiAct) {
         clearROIInternal();
     }
 }
@@ -607,6 +611,8 @@ void JFJochImage::addOverlayItem(QGraphicsItem *item) {
 }
 
 void JFJochImage::DrawROI() {
+    if (!AllowROI())
+        return;
     if (roiBox.isNull() || roiBox.width() <= 0 || roiBox.height() <= 0) return;
 
     auto scn = scene();
@@ -924,99 +930,7 @@ void JFJochImage::updateOverlay() {
 
 void JFJochImage::addCustomOverlay() {}
 
-ROIMessage JFJochImage::accumulateROI(
-    int64_t xmin, int64_t xmax,
-    int64_t ymin, int64_t ymax,
-    const std::function<bool(int64_t, int64_t)> &inside) {
-    int64_t roi_val = 0;
-    uint64_t roi_val_2 = 0;
-    int64_t roi_max = INT64_MIN;
-    uint64_t roi_npixel = 0;
-    uint64_t roi_npixel_masked = 0;
-    float x_weighted = 0.0f;
-    float y_weighted = 0.0f;
 
-    // Clamp bounds defensively to the image
-    xmin = std::max<int64_t>(0, xmin);
-    ymin = std::max<int64_t>(0, ymin);
-    xmax = std::min<int64_t>(W, xmax);
-    ymax = std::min<int64_t>(H, ymax);
-
-    for (int64_t y = ymin; y < ymax; ++y) {
-        for (int64_t x = xmin; x < xmax; ++x) {
-            if (!inside(x, y)) continue;
-
-            float val = image_fp[x + W * y];
-
-            if (std::isinf(val)) {
-                roi_npixel_masked++;
-            } else if (std::isfinite(val)) {
-                x_weighted += val * x;
-                y_weighted += val * y;
-                roi_val += val;
-                roi_val_2 += val * val;
-                if (val > roi_max) roi_max = val;
-                roi_npixel++;
-            }
-        }
-    }
-
-    return ROIMessage{
-        .sum = roi_val,
-        .sum_square = roi_val_2,
-        .max_count = roi_max,
-        .pixels = roi_npixel,
-        .pixels_masked = roi_npixel_masked,
-        .x_weighted = std::lroundf(x_weighted),
-        .y_weighted = std::lroundf(y_weighted),
-    };
-}
-
-void JFJochImage::CalcROI() {
-    if (W*H == 0) {
-        auto msg = ROIMessage{
-            .pixels =  0,
-            .pixels_masked = 0};
-        emit roiCalculated(msg);
-        return;
-    }
-
-    auto box_norm = roiBox.normalized();
-
-    // accumulateROI only reads pixel values inside the box, so an empty ROI needs none
-    if (box_norm.width() > 0 && box_norm.height() > 0)
-        EnsurePixelValues();
-
-    // Using the rectangle as-is; you can adjust inclusivity if needed
-    int64_t xmin = box_norm.left();
-    int64_t xmax = box_norm.right();
-    int64_t ymin = box_norm.top();
-    int64_t ymax = box_norm.bottom();
-
-    ROIMessage msg{};
-    if (roi_type == RoiType::RoiBox)
-        msg = accumulateROI(
-            xmin, xmax, ymin, ymax,
-            [](int64_t, int64_t) { return true; } // everything in the rectangle
-        );
-    else {
-        QPointF delta = roiStartPos - roiEndPos;
-        double radius2 = delta.x() * delta.x() + delta.y() * delta.y();
-        const float cx = static_cast<float>(roiStartPos.x());
-        const float cy = static_cast<float>(roiStartPos.y());
-        const float r2 = static_cast<float>(radius2);
-        msg = accumulateROI(
-            xmin, xmax, ymin, ymax,
-            [cx, cy, r2](int64_t x, int64_t y) {
-                const float dx = static_cast<float>(x) - cx;
-                const float dy = static_cast<float>(y) - cy;
-                const float dist2 = dx * dx + dy * dy;
-                return dist2 <= r2;
-            }
-        );
-    }
-    emit roiCalculated(msg);
-}
 
 void JFJochImage::fitToView() {
     initial_fit_done_ = false;
diff --git a/viewer/image_viewer/JFJochImage.h b/viewer/image_viewer/JFJochImage.h
index acc6ea09..ef83e2f6 100644
--- a/viewer/image_viewer/JFJochImage.h
+++ b/viewer/image_viewer/JFJochImage.h
@@ -91,9 +91,10 @@ class JFJochImage : public QGraphicsView {
     void mouseMoveEvent(QMouseEvent *event) override;
     void mouseReleaseEvent(QMouseEvent *event) override;
 
-    ROIMessage accumulateROI(int64_t xmin, int64_t xmax, int64_t ymin, int64_t ymax,
-                          const std::function<bool(int64_t,int64_t)>& inside);
 protected:
+    // Only the view that owns detector counts offers a region of interest; for the others a
+    // shift-drag would draw a box that means nothing.
+    [[nodiscard]] virtual bool AllowROI() const { return false; }
     virtual void beforeOverlayCleared();
 
     bool show_saturation = false;
@@ -184,6 +185,9 @@ protected:
 
     ResizeHandle hitTestROIHandle(const QPointF& scenePos, qreal tol = 3.0) const;
 
+    // Statistics over roiBox, for the view that has pixel values to accumulate
+    virtual void CalcROI() {}
+
     void updateOverlay();
     void RenderImage();
     PixelColorMap MakeColorMap() const;
@@ -191,9 +195,6 @@ protected:
     // maps image_fp; a subclass whose source is already a compact buffer can map that directly
     // and skip materialising the float image.
     virtual void ColorRow(size_t y, const PixelColorMap &map, QRgb *out) const;
-    // Fill image_fp, which the base class reads for ROI statistics and per-pixel value labels.
-    // Subclasses that colour without it fill it on demand here rather than on every frame.
-    virtual void EnsurePixelValues() {}
     // Re-render once the event queue drains. The foreground slider and the wheel emit far
     // faster than a large image can be recoloured, so intermediate values are dropped
     // instead of queueing a full recolour per event.
@@ -205,7 +206,6 @@ protected:
     // once per scrollbar; the gesture rebuilds it once itself.
     bool suppress_overlay_update_ = false;
     void Redraw();
-    void CalcROI();
 
     // Invalidate image_item_ and overlay tracking after scene()->clear()
     void resetScenePointers();
@@ -228,7 +228,6 @@ signals:
     void writeStatusBar(QString string, int timeout_ms = 0);
     void roiBoxUpdated(QRect box);
     void roiCircleUpdated(double x, double y, double radius);
-    void roiCalculated(ROIMessage &output);
     void viewportChanged(QTransform transform, QPointF center);
     void hoverScenePos(QPointF scenePos);
     // A new frame has been rendered into Frame(). Follower views repaint on this.
diff --git a/viewer/image_viewer/JFJochSimpleImage.cpp b/viewer/image_viewer/JFJochSimpleImage.cpp
index 5e561cfa..2b899f9a 100644
--- a/viewer/image_viewer/JFJochSimpleImage.cpp
+++ b/viewer/image_viewer/JFJochSimpleImage.cpp
@@ -30,14 +30,12 @@ void JFJochSimpleImage::setImage(std::shared_ptr<const SimpleImage> img) {
         loadImageInternal();
         RenderImage();
         Redraw();
-        CalcROI();
     } else {
         image_.reset();
         W = 0; H = 0;
         if (scene())
             scene()->clear();
         resetScenePointers();
-        CalcROI();
     }
 }
 
diff --git a/viewer/windows/JFJoch2DAzintImageWindow.cpp b/viewer/windows/JFJoch2DAzintImageWindow.cpp
index 062328a1..287fafc4 100644
--- a/viewer/windows/JFJoch2DAzintImageWindow.cpp
+++ b/viewer/windows/JFJoch2DAzintImageWindow.cpp
@@ -3,7 +3,6 @@
 
 #include <QStatusBar>
 #include "JFJoch2DAzintImageWindow.h"
-#include "../widgets/JFJochViewerROIResult.h"
 
 JFJoch2DAzintImageWindow::JFJoch2DAzintImageWindow(QWidget *parent) : JFJochHelperWindow(parent) {
     QWidget *centralWidget = new QWidget(this);
@@ -25,12 +24,9 @@ JFJoch2DAzintImageWindow::JFJoch2DAzintImageWindow(QWidget *parent) : JFJochHelp
     foreground_row->addWidget(new QLabel("Foreground:"));
     foreground_row->addWidget(foreground_slider);
 
-    auto roi_result = new JFJochViewerROIResult(this);
-
     grid_layout->addLayout(background_row, 0, 0, 1, 2);
     grid_layout->addLayout(foreground_row, 1, 0, 1, 2);
     grid_layout->addWidget(viewer, 2, 0, 1, 2);
-    grid_layout->addWidget(roi_result, 3, 0, 1, 2);
     centralWidget->setLayout(grid_layout);
 
     connect(viewer, &JFJochAzIntImage::backgroundChanged,
@@ -45,8 +41,6 @@ JFJoch2DAzintImageWindow::JFJoch2DAzintImageWindow(QWidget *parent) : JFJochHelp
                 foreground_slider->setValue(val);
             });
 
-    connect(viewer, &JFJochAzIntImage::roiCalculated, roi_result, &JFJochViewerROIResult::SetROIResult);
-
     connect(background_slider, &SliderPlusBox::valueChanged, viewer, &JFJochAzIntImage::changeBackground);
     connect(foreground_slider, &SliderPlusBox::valueChanged, viewer, &JFJochAzIntImage::changeForeground);
 
diff --git a/viewer/windows/JFJochCalibrationWindow.cpp b/viewer/windows/JFJochCalibrationWindow.cpp
index 05ffc281..2033f45d 100644
--- a/viewer/windows/JFJochCalibrationWindow.cpp
+++ b/viewer/windows/JFJochCalibrationWindow.cpp
@@ -7,7 +7,6 @@
 #include <QHBoxLayout>
 #include <QLabel>
 
-#include "../widgets/JFJochViewerROIResult.h"
 
 JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelperWindow(parent) {
     QWidget *centralWidget = new QWidget(this);
@@ -37,14 +36,11 @@ JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelper
     foreground_row->addWidget(new QLabel("Foreground:"));
     foreground_row->addWidget(foreground_slider);
 
-    auto roi_result = new JFJochViewerROIResult(this);
-
     grid_layout->addWidget(calibration_option, 0, 0);
     grid_layout->addWidget(color_map_select, 0, 1);
     grid_layout->addLayout(background_row, 1, 0, 1, 2);
     grid_layout->addLayout(foreground_row, 2, 0, 1, 2);
     grid_layout->addWidget(viewer, 3, 0, 1, 2);
-    grid_layout->addWidget(roi_result, 4, 0, 1, 2);
 
     connect(viewer, &JFJochSimpleImage::backgroundChanged,
         [this] (float val) {
@@ -57,8 +53,6 @@ JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelper
             QSignalBlocker blocker(foreground_slider);
             foreground_slider->setValue(val);
         });
-    connect(viewer, &JFJochSimpleImage::roiCalculated, roi_result, &JFJochViewerROIResult::SetROIResult);
-
     connect(background_slider, &SliderPlusBox::valueChanged, viewer, &JFJochSimpleImage::changeBackground);
     connect(foreground_slider, &SliderPlusBox::valueChanged, viewer, &JFJochSimpleImage::changeForeground);