diff --git a/image.frag b/image.frag
index 71b2eaf..e7fa6fa 100644
--- a/image.frag
+++ b/image.frag
@@ -6,9 +6,16 @@ uniform vec2 scale;
 uniform float a;
 uniform int stretch;
 
+float asinh_(float x)
+{
+    return log(x + sqrt(x*x + 1.0f));
+}
+
 void main(void)
 {
     vec4 color = texture2D(qt_Texture0, qt_TexCoord0);
+    color = color*scale.x + scale.y;
+    max(color, vec4(0.0f));
 
     switch(stretch)
     {
@@ -25,13 +32,15 @@ void main(void)
         break;
     case 4:
     {
-        float l = color.r*0.2126f + color.g*0.7152f + color.b*0.7152f;
-        color *= asinh(l / a) / asinh(1 / a);
+        //float l = color.r*0.2126f + color.g*0.7152f + color.b*0.0722f;
+        float l = (color.r+color.g+color.b)*0.33333f;
+        float k = asinh(l*a)/(l*asinh(a));
+        color *= k;
     }
         break;
     }
 
-    color = color*scale.x + scale.y;
+    //color = color*scale.x + scale.y;
     //float color = pow(c, 0.4545);
     gl_FragColor = color;
 }
diff --git a/imagescrollareagl.cpp b/imagescrollareagl.cpp
index eebb6dd..65f7d67 100644
--- a/imagescrollareagl.cpp
+++ b/imagescrollareagl.cpp
@@ -113,6 +113,7 @@ void ImageWidget::setStrech(int stretch)
 
 void ImageWidget::setStretchParam(float param)
 {
+    qDebug() << param;
     m_param = param;
     update();
 }
@@ -127,11 +128,10 @@ void ImageWidget::setOffset(int dx, int dy)
 void ImageWidget::paintGL()
 {
     if(m_blockRepaint)return;
-    qDebug() << "PAINT";
+    qDebug() << "PAINT" << m_param;
 
     float dx = m_dx;
     float dy = m_dy;
-    qDebug() << "dxy" << dx << dy;
     if(width() > m_image->width()*m_scale)
         dx = -width()*0.5f + m_image->width()*m_scale*0.5f;
     if(height() > m_image->height()*m_scale)
@@ -281,7 +281,6 @@ void ImageScrollAreaGL::updateScrollbars(bool zoom)
 void ImageScrollAreaGL::resizeEvent(QResizeEvent *event)
 {
     QWidget::resizeEvent(event);
-    qDebug() << "resize" << m_imageWidget->size();
     m_verticalScrollBar->setPageStep(m_imageWidget->height());
     m_horizontalScrollBar->setPageStep(m_imageWidget->width());
     updateScrollbars();
@@ -341,6 +340,5 @@ void ImageScrollAreaGL::oneToOne()
 
 void ImageScrollAreaGL::scrollEvent()
 {
-    qDebug() << m_horizontalScrollBar->value() << m_verticalScrollBar->value();
     m_imageWidget->setOffset(m_horizontalScrollBar->value(), m_verticalScrollBar->value());
 }
diff --git a/stretchpanel.cpp b/stretchpanel.cpp
index a049fec..6a83550 100644
--- a/stretchpanel.cpp
+++ b/stretchpanel.cpp
@@ -37,13 +37,14 @@ void StretchPanel::calculateParam()
     switch(m_stretchSelect->currentIndex())
     {
     case 2:
-        param = val*10/UINT16_MAX;
+        param = val*100/UINT16_MAX;
         break;
     case 3:
         param = val;
         break;
     case 4:
-        param = 1.001-val/UINT16_MAX;
+        val += 100;
+        param = val/100.0f;
         break;
     default:
         return;