Fix ImageView levelMode (#1974)

* fixes #1769

* Automatically set image to ImageView if imageItem is provided.
Added a test for correct initialization of ImageView with imageItem and levelMode.

pyqtgraph/graphicsItems/HistogramLUTItem.py

@@ -443,7 +443,7 @@ class HistogramLUTItem(GraphicsWidget):
             self.regions[i].setVisible(False)
 
         if self.levelMode == 'rgba':
-            imax = 4
+            nch = 4
             if self.imageItem() is not None:
                 # Only show rgb channels if connected image lacks alpha.
                 nch = self.imageItem().channels()

pyqtgraph/imageview/ImageView.py

@@ -127,7 +127,6 @@ class ImageView(QtGui.QWidget):
         self.ui = ui_template.Ui_Form()
         self.ui.setupUi(self)
         self.scene = self.ui.graphicsView.scene()
-        self.ui.histogram.setLevelMode(levelMode)
         
         self.ignorePlaying = False
         
@@ -139,15 +138,6 @@ class ImageView(QtGui.QWidget):
         self.view.setAspectLocked(True)
         self.view.invertY()
         
-        if imageItem is None:
-            self.imageItem = ImageItem()
-        else:
-            self.imageItem = imageItem
-        self.view.addItem(self.imageItem)
-        self.currentIndex = 0
-        
-        self.ui.histogram.setImageItem(self.imageItem)
-        
         self.menu = None
         
         self.ui.normGroup.hide()
@@ -171,6 +161,18 @@ class ImageView(QtGui.QWidget):
         self.timeLine.setZValue(1)
         self.ui.roiPlot.addItem(self.timeLine)
         self.ui.splitter.setSizes([self.height()-35, 35])
+
+        # init imageItem and histogram
+        if imageItem is None:
+            self.imageItem = ImageItem()
+        else:
+            self.imageItem = imageItem
+            self.setImage(imageItem.image, autoRange=False, autoLevels=False, transform=imageItem.transform())
+        self.view.addItem(self.imageItem)
+        self.currentIndex = 0
+        
+        self.ui.histogram.setImageItem(self.imageItem)
+        self.ui.histogram.setLevelMode(levelMode)
         
         # make splitter an unchangeable small grey line:
         s = self.ui.splitter

tests/imageview/test_imageview.py

@@ -10,3 +10,9 @@ def test_nan_image():
     v.imageItem.getHistogram()
     app.processEvents()
     v.window().close()
+
+def test_init_with_mode_and_imageitem():
+    data = np.random.randint(256, size=(256, 256, 3))
+    imgitem = pg.ImageItem(data)
+    pg.ImageView(imageItem=imgitem, levelMode="rgba")
+    assert(pg.image is not None)