diff --git a/pyqtgraph/__init__.py b/pyqtgraph/__init__.py
index 1468bbdd..49b918d9 100644
--- a/pyqtgraph/__init__.py
+++ b/pyqtgraph/__init__.py
@@ -395,7 +395,7 @@ def plot(*args, **kargs):
     Accepts a *title* argument to set the title of the window.
     All other arguments are used to plot data. (see :func:`PlotItem.plot() <pyqtgraph.PlotItem.plot>`)
     """
-    mkQApp()      
+    mkQApp()
     pwArgList = ['title', 'labels', 'name', 'left', 'right', 'top', 'bottom', 'background']
     pwArgs = {}
     dataArgs = {}
diff --git a/pyqtgraph/functions.py b/pyqtgraph/functions.py
index 7276f677..836d96cf 100644
--- a/pyqtgraph/functions.py
+++ b/pyqtgraph/functions.py
@@ -1129,7 +1129,7 @@ def makeARGB(data, lut=None, levels=None, scale=None, useRGBA=False, output=None
             raise Exception('levels argument is required for float input types')
     if not isinstance(levels, xp.ndarray):
         levels = xp.array(levels)
-    levels = levels.astype(xp.float32)
+    levels = levels.astype(xp.float64)
     if levels.ndim == 1:
         if levels.shape[0] != 2:
             raise Exception('levels argument must have length 2')
diff --git a/pyqtgraph/graphicsItems/PlotDataItem.py b/pyqtgraph/graphicsItems/PlotDataItem.py
index f4654f79..9e9431ff 100644
--- a/pyqtgraph/graphicsItems/PlotDataItem.py
+++ b/pyqtgraph/graphicsItems/PlotDataItem.py
@@ -9,7 +9,6 @@ from .ScatterPlotItem import ScatterPlotItem
 from .. import functions as fn
 from .. import debug as debug
 from .. import getConfigOption
-import warnings
 
 
 class PlotDataItem(GraphicsObject):