diff --git a/imagescrollareagl.cpp b/imagescrollareagl.cpp
index a2dde9c..7c7bff1 100644
--- a/imagescrollareagl.cpp
+++ b/imagescrollareagl.cpp
@@ -57,6 +57,10 @@ ImageWidget::ImageWidget(QWidget *parent) : QOpenGLWidget(parent)
     m_superpixel = m_invert = false;
     m_showThumbnails = false;
     m_thumbnailCount = 0;
+    m_updateTimer = new QTimer(this);
+    m_updateTimer->setInterval(500);
+    m_updateTimer->setSingleShot(true);
+    connect(m_updateTimer, SIGNAL(timeout()), this, SLOT(update()));
     setAcceptDrops(true);
 }
 
@@ -190,7 +194,7 @@ void ImageWidget::thumbnailLoaded(const Image *image)
     int sizes[3] = { std::max(1, a > 1.0f ? THUMB_SIZE : (int)(THUMB_SIZE * a)), std::max(1, a < 1.0f ? THUMB_SIZE : (int)(THUMB_SIZE / a)), image->number() };
     m_bufferSizes->bind();
     m_bufferSizes->write(image->number() * sizeof(sizes), sizes, sizeof(sizes));
-    update();
+    if(!m_updateTimer->isActive())m_updateTimer->start();
 }
 
 void ImageWidget::showThumbnail(bool enable)
@@ -218,7 +222,7 @@ void ImageWidget::paintGL()
         f->glUniform3i(m_thumbnailProgram->uniformLocation("viewport_row"), width(), height(), width()/THUMB_SIZE_BORDER);
         m_thumbnailProgram->setUniformValue("mtf_param", m_low, m_mid, m_high);
         m_thumbnailProgram->setUniformValue("invert", m_invert);
-        m_thumbnailProgram->setUniformValue("offset", m_dx, m_dy);
+        m_thumbnailProgram->setUniformValue("offset", 0, m_dy);
         f3->glVertexAttribDivisor(m_thumbnailProgram->attributeLocation("imageSize_num"), 1);
         QMatrix4x4 mvp;
         mvp.ortho(rect());
@@ -428,8 +432,8 @@ void ImageScrollAreaGL::setThumbnails(int count)
     m_thumbCount = count;
     if(m_thumbCount)
     {
-        m_verticalScrollBar->setRange(0, (m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) + 1) * THUMB_SIZE_BORDER);
-        m_verticalScrollBar->setPageStep(THUMB_SIZE);
+        m_verticalScrollBar->setRange(0, m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) * THUMB_SIZE_BORDER);
+        m_verticalScrollBar->setPageStep(THUMB_SIZE_BORDER);
     }
     else
     {
@@ -445,8 +449,8 @@ void ImageScrollAreaGL::updateScrollbars(bool zoom)
     {
         m_horizontalScrollBar->hide();
         m_verticalScrollBar->show();
-        m_verticalScrollBar->setRange(0, (m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) + 1) * THUMB_SIZE_BORDER);
-        m_verticalScrollBar->setPageStep(128);
+        m_verticalScrollBar->setRange(0, m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) * THUMB_SIZE_BORDER);
+        m_verticalScrollBar->setPageStep(THUMB_SIZE_BORDER);
     }
     else
     {
@@ -468,8 +472,8 @@ void ImageScrollAreaGL::resizeEvent(QResizeEvent *event)
     QWidget::resizeEvent(event);
     if(m_thumbCount)
     {
-        m_verticalScrollBar->setRange(0, (m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) + 1) * THUMB_SIZE_BORDER);
-        m_verticalScrollBar->setPageStep(128);
+        m_verticalScrollBar->setRange(0, m_thumbCount / (m_imageWidget->width() / THUMB_SIZE_BORDER) * THUMB_SIZE_BORDER);
+        m_verticalScrollBar->setPageStep(THUMB_SIZE_BORDER);
     }
     else
     {
diff --git a/imagescrollareagl.h b/imagescrollareagl.h
index 5a80fdf..dc0c924 100644
--- a/imagescrollareagl.h
+++ b/imagescrollareagl.h
@@ -10,6 +10,7 @@
 #include <QOpenGLTexture>
 #include <QOpenGLVertexArrayObject>
 #include <QScrollBar>
+#include <QTimer>
 #include "rawimage.h"
 #include "imageringlist.h"
 
@@ -27,6 +28,7 @@ class ImageWidget : public QOpenGLWidget
     Q_OBJECT
     QOpenGLFunctions *f;
     QOpenGLFunctions_3_3_Core *f3;
+    QTimer *m_updateTimer;
     std::unique_ptr<QOpenGLShaderProgram> m_program;
     std::unique_ptr<QOpenGLShaderProgram> m_thumbnailProgram;
     std::unique_ptr<QOpenGLBuffer> m_buffer;