From 65c1d4eec674103a59d69e3fe21762df44c236de Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Sat, 27 Dec 2014 10:52:27 -0600
Subject: [PATCH] Update viewer for PyQt5 compatibility

Conflicts:
	skimage/viewer/tests/test_plugins.py
	skimage/viewer/tests/test_tools.py
---
 skimage/__init__.py                       |  8 ++++-
 skimage/viewer/__init__.py                | 14 +++------
 skimage/viewer/canvastools/base.py        |  5 +--
 skimage/viewer/canvastools/linetool.py    |  5 +--
 skimage/viewer/canvastools/painttool.py   | 11 +++----
 skimage/viewer/canvastools/recttool.py    |  6 +---
 skimage/viewer/plugins/base.py            | 16 +++-------
 skimage/viewer/plugins/color_histogram.py |  5 +--
 skimage/viewer/plugins/plotplugin.py      |  2 +-
 skimage/viewer/qt.py                      |  8 +++++
 skimage/viewer/qt/QtCore.py               | 22 -------------
 skimage/viewer/qt/QtGui.py                | 11 -------
 skimage/viewer/qt/README.rst              |  5 ---
 skimage/viewer/qt/__init__.py             | 22 -------------
 skimage/viewer/tests/test_plugins.py      | 33 +++++++++++++-------
 skimage/viewer/tests/test_tools.py        | 30 ++++++++++++++++++
 skimage/viewer/tests/test_utils.py        | 20 ++++++------
 skimage/viewer/tests/test_viewer.py       | 15 +++++----
 skimage/viewer/tests/test_widgets.py      | 27 +++++++++-------
 skimage/viewer/utils/core.py              | 31 ++++++------------
 skimage/viewer/utils/dialogs.py           |  2 +-
 skimage/viewer/viewers/core.py            | 32 ++++++++-----------
 skimage/viewer/widgets/core.py            | 38 ++++++++++-------------
 skimage/viewer/widgets/history.py         |  4 +--
 24 files changed, 161 insertions(+), 211 deletions(-)
 create mode 100644 skimage/viewer/qt.py
 delete mode 100644 skimage/viewer/qt/QtCore.py
 delete mode 100644 skimage/viewer/qt/QtGui.py
 delete mode 100644 skimage/viewer/qt/README.rst
 delete mode 100644 skimage/viewer/qt/__init__.py

diff --git a/skimage/__init__.py b/skimage/__init__.py
index fb38f87a..031ae075 100644
--- a/skimage/__init__.py
+++ b/skimage/__init__.py
@@ -60,7 +60,13 @@ import os.path as _osp
 import imp as _imp
 import functools as _functools
 import warnings as _warnings
-from skimage._shared.utils import deprecated as _deprecated
+
+import matplotlib as _mpl
+try:
+    _imp.find_module('PyQt5')
+    _mpl.use('Qt5Agg')
+except ImportError:
+    _mpl.use('Qt4Agg')
 
 pkg_dir = _osp.abspath(_osp.dirname(__file__))
 data_dir = _osp.join(pkg_dir, 'data')
diff --git a/skimage/viewer/__init__.py b/skimage/viewer/__init__.py
index 4bf70a93..365e00a2 100644
--- a/skimage/viewer/__init__.py
+++ b/skimage/viewer/__init__.py
@@ -1,11 +1,7 @@
-from warnings import warn
-from skimage._shared.version_requirements import is_installed
+try:
+    from .qt import QtGui as _QtGui
+except ImportError as e:
+    raise
+    raise ImportError('Viewer requires Qt')
 
 from .viewers import ImageViewer, CollectionViewer
-from .qt import qt_api
-
-viewer_available = not qt_api is None and is_installed('matplotlib')
-if not viewer_available:
-    warn('Viewer requires matplotlib and Qt')
-
-del qt_api, is_installed, warn
diff --git a/skimage/viewer/canvastools/base.py b/skimage/viewer/canvastools/base.py
index 197800c0..4b1d0c00 100644
--- a/skimage/viewer/canvastools/base.py
+++ b/skimage/viewer/canvastools/base.py
@@ -1,8 +1,5 @@
 import numpy as np
-try:
-    from matplotlib import lines
-except ImportError:
-    pass
+from matplotlib import lines
 
 __all__ = ['CanvasToolBase', 'ToolHandles']
 
diff --git a/skimage/viewer/canvastools/linetool.py b/skimage/viewer/canvastools/linetool.py
index f18a1915..58b05bc4 100644
--- a/skimage/viewer/canvastools/linetool.py
+++ b/skimage/viewer/canvastools/linetool.py
@@ -1,9 +1,6 @@
 import numpy as np
 
-try:
-    from matplotlib import lines
-except ImportError:
-    pass
+from matplotlib import lines
 from skimage.viewer.canvastools.base import CanvasToolBase, ToolHandles
 
 
diff --git a/skimage/viewer/canvastools/painttool.py b/skimage/viewer/canvastools/painttool.py
index 953f6ebe..9f4bb8ec 100644
--- a/skimage/viewer/canvastools/painttool.py
+++ b/skimage/viewer/canvastools/painttool.py
@@ -1,11 +1,8 @@
 import numpy as np
-try:
-    import matplotlib.pyplot as plt
-    import matplotlib.colors as mcolors
-    LABELS_CMAP = mcolors.ListedColormap(['white', 'red', 'dodgerblue', 'gold',
-                                          'greenyellow', 'blueviolet'])
-except ImportError:
-    pass
+import matplotlib.pyplot as plt
+import matplotlib.colors as mcolors
+LABELS_CMAP = mcolors.ListedColormap(['white', 'red', 'dodgerblue', 'gold',
+                                      'greenyellow', 'blueviolet'])
 from skimage.viewer.canvastools.base import CanvasToolBase
 
 
diff --git a/skimage/viewer/canvastools/recttool.py b/skimage/viewer/canvastools/recttool.py
index 4acccf8a..4520584e 100644
--- a/skimage/viewer/canvastools/recttool.py
+++ b/skimage/viewer/canvastools/recttool.py
@@ -1,8 +1,4 @@
-try:
-    from matplotlib.widgets import RectangleSelector
-except ImportError:
-    RectangleSelector = object
-
+from matplotlib.widgets import RectangleSelector
 from skimage.viewer.canvastools.base import CanvasToolBase
 from skimage.viewer.canvastools.base import ToolHandles
 
diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index def0bfd9..7b0418b2 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -4,19 +4,11 @@ Base class for Plugins that interact with ImageViewer.
 from warnings import warn
 
 import numpy as np
-
-from ..qt import QtGui, qt_api
-from ..qt.QtCore import Qt, Signal
+from ..qt import QtWidgets, QtCore, Signal
 from ..utils import RequiredAttr, init_qtapp
-from skimage._shared.testing import doctest_skip_parser
-
-if qt_api is not None:
-    has_qt = True
-else:
-    has_qt = False
 
 
-class Plugin(QtGui.QDialog):
+class Plugin(QtWidgets.QDialog):
     """Base class for plugins that interact with an ImageViewer.
 
     A plugin connects an image filter (or another function) to an image viewer.
@@ -101,7 +93,7 @@ class Plugin(QtGui.QDialog):
                  "then the `image_filter` argument is ignored.")
 
         self.setWindowTitle(self.name)
-        self.layout = QtGui.QGridLayout(self)
+        self.layout = QtWidgets.QGridLayout(self)
         self.resize(width, height)
         self.row = 0
 
@@ -124,7 +116,7 @@ class Plugin(QtGui.QDialog):
         the image matches the filtered value specified by attached widgets.
         """
         self.setParent(image_viewer)
-        self.setWindowFlags(Qt.Dialog)
+        self.setWindowFlags(QtCore.Qt.Dialog)
 
         self.image_viewer = image_viewer
         self.image_viewer.plugins.append(self)
diff --git a/skimage/viewer/plugins/color_histogram.py b/skimage/viewer/plugins/color_histogram.py
index 52c71786..d6c6ddfc 100644
--- a/skimage/viewer/plugins/color_histogram.py
+++ b/skimage/viewer/plugins/color_histogram.py
@@ -1,8 +1,5 @@
 import numpy as np
-try:
-    import matplotlib.pyplot as plt
-except ImportError:
-    pass
+import matplotlib.pyplot as plt
 from skimage import color
 from skimage import exposure
 from .plotplugin import PlotPlugin
diff --git a/skimage/viewer/plugins/plotplugin.py b/skimage/viewer/plugins/plotplugin.py
index 5de6be7b..f995efa8 100644
--- a/skimage/viewer/plugins/plotplugin.py
+++ b/skimage/viewer/plugins/plotplugin.py
@@ -1,6 +1,6 @@
 import numpy as np
-from ..qt import QtGui
 
+from ..qt import QtGui
 from ..utils import new_plot
 from .base import Plugin
 
diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
new file mode 100644
index 00000000..bc827f9a
--- /dev/null
+++ b/skimage/viewer/qt.py
@@ -0,0 +1,8 @@
+try:
+    from matplotlib.backends.qt_compat import QtGui, QtCore, QtWidgets
+except ImportError:
+    from matplotlib.backends.qt4_compat import QtGui, QtCore
+    QtWidgets = QtGui
+
+Qt = QtCore.Qt
+Signal = QtCore.Signal
diff --git a/skimage/viewer/qt/QtCore.py b/skimage/viewer/qt/QtCore.py
deleted file mode 100644
index 19b92a53..00000000
--- a/skimage/viewer/qt/QtCore.py
+++ /dev/null
@@ -1,22 +0,0 @@
-from . import qt_api
-
-if qt_api == 'pyside':
-    from PySide.QtCore import *
-elif qt_api == 'pyqt':
-    from PyQt4.QtCore import *
-    # Use pyside names for signals and slots
-    Signal = pyqtSignal
-    Slot = pyqtSlot
-else:
-    # Mock objects for buildbot (which doesn't have Qt, but imports viewer).
-    class Qt(object):
-        TopDockWidgetArea = None
-        BottomDockWidgetArea = None
-        LeftDockWidgetArea = None
-        RightDockWidgetArea = None
-
-    def Signal(*args, **kwargs):
-        pass
-
-    def Slot(*args, **kwargs):
-        pass
diff --git a/skimage/viewer/qt/QtGui.py b/skimage/viewer/qt/QtGui.py
deleted file mode 100644
index 12e9837f..00000000
--- a/skimage/viewer/qt/QtGui.py
+++ /dev/null
@@ -1,11 +0,0 @@
-from . import qt_api
-
-if qt_api == 'pyside':
-    from PySide.QtGui import *
-elif qt_api == 'pyqt':
-    from PyQt4.QtGui import *
-else:
-    # Mock objects
-    QMainWindow = object
-    QDialog = object
-    QWidget = object
diff --git a/skimage/viewer/qt/README.rst b/skimage/viewer/qt/README.rst
deleted file mode 100644
index 993ae1a5..00000000
--- a/skimage/viewer/qt/README.rst
+++ /dev/null
@@ -1,5 +0,0 @@
-This qt subpackage provides a wrapper to allow use of either PySide or PyQt4.
-In addition, if neither package is available, some mock objects are created to
-prevent errors in the TravisCI build. Only the objects used in the global
-namespace need to be mocked (e.g., a Qt object that gets subclassed is used
-in the global namespace).
diff --git a/skimage/viewer/qt/__init__.py b/skimage/viewer/qt/__init__.py
deleted file mode 100644
index 2fc4e946..00000000
--- a/skimage/viewer/qt/__init__.py
+++ /dev/null
@@ -1,22 +0,0 @@
-import os
-import warnings
-
-qt_api = os.environ.get('QT_API')
-
-if qt_api is None:
-    try:
-        import PyQt4
-        qt_api = 'pyqt'
-    except ImportError:
-        try:
-            import PySide
-            qt_api = 'pyside'
-        except ImportError:
-            qt_api = None
-            # Note that we don't want to raise an error because that would
-            # cause the TravisCI build to fail.
-            warnings.warn("Could not import PyQt4: ImageViewer not available!")
-
-
-if qt_api is not None:
-    os.environ['QT_API'] = qt_api
diff --git a/skimage/viewer/tests/test_plugins.py b/skimage/viewer/tests/test_plugins.py
index 528df8f4..b5cf7ab9 100644
--- a/skimage/viewer/tests/test_plugins.py
+++ b/skimage/viewer/tests/test_plugins.py
@@ -4,15 +4,26 @@ import skimage
 import skimage.data as data
 from skimage.filters.rank import median
 from skimage.morphology import disk
-from skimage.viewer import ImageViewer, viewer_available
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.plugins.base import Plugin
+    from skimage.viewer.widgets import Slider
+    from skimage.viewer.plugins import (
+        LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
+        PlotPlugin)
+except ImportError:
+    ImageViewer is None
 from numpy.testing import assert_equal, assert_allclose, assert_almost_equal
 from numpy.testing.decorators import skipif
+<<<<<<< HEAD
 from skimage.viewer.plugins import (
     LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
     PlotPlugin)
 from skimage.viewer.plugins.base import Plugin
 from skimage.viewer.widgets import Slider
 from skimage._shared._warnings import expected_warnings
+=======
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 
 
 def setup_line_profile(image, limits='image'):
@@ -22,7 +33,7 @@ def setup_line_profile(image, limits='image'):
     return plugin
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile():
     """ Test a line profile using an ndim=2 image"""
     plugin = setup_line_profile(data.camera())
@@ -36,7 +47,7 @@ def test_line_profile():
     assert_allclose(scan_data.mean(), 0.2812, rtol=1e-3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile_rgb():
     """ Test a line profile using an ndim=3 image"""
     plugin = setup_line_profile(data.chelsea(), limits=None)
@@ -51,7 +62,7 @@ def test_line_profile_rgb():
     assert_allclose(scan_data.mean(), 0.4359, rtol=1e-3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_line_profile_dynamic():
     """Test a line profile updating after an image transform"""
     image = data.coins()[:-50, :]  # shave some off to make the line lower
@@ -77,7 +88,7 @@ def test_line_profile_dynamic():
     assert_almost_equal(np.max(line) - np.min(line), 0.639, 1)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_measure():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -89,7 +100,7 @@ def test_measure():
     assert_equal(str(m._angle.text[:5]), '135.0')
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_canny():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -102,7 +113,7 @@ def test_canny():
     assert edges.sum() == 2852
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_label_painter():
     image = data.camera()
     moon = data.moon()
@@ -120,7 +131,7 @@ def test_label_painter():
     assert_equal(lp.paint_tool.shape, moon.shape)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_crop():
     image = data.camera()
     viewer = ImageViewer(image)
@@ -131,7 +142,7 @@ def test_crop():
     assert_equal(viewer.image.shape, (101, 101))
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_color_histogram():
     image = skimage.img_as_float(data.load('color.png'))
     viewer = ImageViewer(image)
@@ -143,7 +154,7 @@ def test_color_histogram():
     assert_almost_equal(viewer.image.std(), 0.325, 3)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_plot_plugin():
     viewer = ImageViewer(data.moon())
     plugin = PlotPlugin(image_filter=lambda x: x)
@@ -155,7 +166,7 @@ def test_plot_plugin():
     viewer.close()
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_plugin():
     img = skimage.img_as_float(data.moon())
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_tools.py b/skimage/viewer/tests/test_tools.py
index 6b923063..6ea25940 100644
--- a/skimage/viewer/tests/test_tools.py
+++ b/skimage/viewer/tests/test_tools.py
@@ -4,12 +4,22 @@ import numpy as np
 from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
 from skimage import data
+<<<<<<< HEAD
 from skimage.viewer import ImageViewer, viewer_available
 from skimage.viewer.canvastools import (
     LineTool, ThickLineTool, RectangleTool, PaintTool)
 from skimage.viewer.canvastools.base import CanvasToolBase
 from matplotlib.testing.decorators import cleanup
 
+=======
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.canvastools import (
+        LineTool, ThickLineTool, RectangleTool, PaintTool)
+    from skimage.viewer.canvastools.base import CanvasToolBase
+except ImportError:
+    ImageViewer = None
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 
 
 def get_end_points(image):
@@ -74,8 +84,12 @@ def do_event(viewer, etype, button=1, xdata=0, ydata=0, key=None):
     func(event)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -100,8 +114,12 @@ def test_line_tool():
     assert_equal(tool.geometry, np.array([[100, 100], [10, 10]]))
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_thick_line_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -124,8 +142,12 @@ def test_thick_line_tool():
     assert_equal(tool.linewidth, 1)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_rect_tool():
     img = data.camera()
     viewer = ImageViewer(img)
@@ -153,8 +175,12 @@ def test_rect_tool():
     assert_equal(tool.geometry, [10, 100,  10, 100])
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_paint_tool():
     img = data.moon()
     viewer = ImageViewer(img)
@@ -187,8 +213,12 @@ def test_paint_tool():
     assert_equal(tool.overlay.sum(), 0)
 
 
+<<<<<<< HEAD
 @cleanup
 @skipif(not viewer_available)
+=======
+@skipif(ImageViewer is None)
+>>>>>>> 7e2fdf7... Update viewer for PyQt5 compatibility
 def test_base_tool():
     img = data.moon()
     viewer = ImageViewer(img)
diff --git a/skimage/viewer/tests/test_utils.py b/skimage/viewer/tests/test_utils.py
index 77f30299..5c962e5c 100644
--- a/skimage/viewer/tests/test_utils.py
+++ b/skimage/viewer/tests/test_utils.py
@@ -1,14 +1,14 @@
 # -*- coding: utf-8 -*-
-from skimage.viewer import viewer_available
-from skimage.viewer.qt import QtCore, QtGui
-from skimage.viewer import utils
-from skimage.viewer.utils import dialogs
+try:
+    from skimage.viewer import utils
+    from skimage.viewer.utils import dialogs
+    from skimage.viewer.qt import QtCore, QtGui
+except ImportError:
+    QtCore = None
 from numpy.testing.decorators import skipif
-from skimage.viewer import utils
-from skimage.viewer.utils import dialogs
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_event_loop():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -16,7 +16,7 @@ def test_event_loop():
     utils.start_qtapp()
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_format_filename():
     fname = dialogs._format_filename(('apple', 2))
     assert fname == 'apple'
@@ -24,7 +24,7 @@ def test_format_filename():
     assert fname is None
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_open_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
@@ -33,7 +33,7 @@ def test_open_file_dialog():
     assert filename is None
 
 
-@skipif(not viewer_available)
+@skipif(QtCore is None)
 def test_save_file_dialog():
     utils.init_qtapp()
     timer = QtCore.QTimer()
diff --git a/skimage/viewer/tests/test_viewer.py b/skimage/viewer/tests/test_viewer.py
index 1604ca6d..0709d18d 100644
--- a/skimage/viewer/tests/test_viewer.py
+++ b/skimage/viewer/tests/test_viewer.py
@@ -1,9 +1,12 @@
 
 from skimage import data
-from skimage.viewer.qt import QtGui, QtCore
-from skimage.viewer import ImageViewer, CollectionViewer, viewer_available
+try:
+    from skimage.viewer.qt import QtGui, QtCore
+    from skimage.viewer import ImageViewer, CollectionViewer
+    from skimage.viewer.plugins import OverlayPlugin
+except ImportError:
+    ImageViewer = None
 from skimage.transform import pyramid_gaussian
-from skimage.viewer.plugins import OverlayPlugin
 from skimage.filters import sobel
 from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
@@ -11,7 +14,7 @@ from skimage._shared.version_requirements import is_installed
 from skimage._shared._warnings import expected_warnings
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_viewer():
     astro = data.astronaut()
     coins = data.coins()
@@ -38,7 +41,7 @@ def make_key_event(key):
                            QtCore.Qt.NoModifier)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_collection_viewer():
 
     img = data.astronaut()
@@ -54,7 +57,7 @@ def test_collection_viewer():
     view._format_coord(10, 10)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 @skipif(not is_installed('matplotlib', '>=1.2'))
 def test_viewer_with_overlay():
     img = data.coins()
diff --git a/skimage/viewer/tests/test_widgets.py b/skimage/viewer/tests/test_widgets.py
index 170c186c..8e76d29b 100644
--- a/skimage/viewer/tests/test_widgets.py
+++ b/skimage/viewer/tests/test_widgets.py
@@ -1,11 +1,14 @@
 
 import os
 from skimage import data, img_as_float, io, img_as_uint
-from skimage.viewer import ImageViewer, viewer_available
-from skimage.viewer.widgets import (
-    Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
-from skimage.viewer.plugins.base import Plugin
-from skimage.viewer.qt import QtGui, QtCore
+try:
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.qt import QtGui, QtCore
+    from skimage.viewer.widgets import (
+        Slider, OKCancelButtons, SaveButtons, ComboBox, CheckBox, Text)
+    from skimage.viewer.plugins.base import Plugin
+except ImportError:
+    ImageViewer = None
 from numpy.testing import assert_almost_equal, assert_equal
 from numpy.testing.decorators import skipif
 from skimage._shared._warnings import expected_warnings
@@ -18,7 +21,7 @@ def get_image_viewer():
     return viewer
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_check_box():
     viewer = get_image_viewer()
     cb = CheckBox('hello', value=True, alignment='left')
@@ -33,7 +36,7 @@ def test_check_box():
     assert_equal(cb.val, False)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_combo_box():
     viewer = get_image_viewer()
     cb = ComboBox('hello', ('a', 'b', 'c'))
@@ -46,7 +49,7 @@ def test_combo_box():
     assert_equal(cb.index, 2)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_text_widget():
     viewer = get_image_viewer()
     txt = Text('hello', 'hello, world!')
@@ -57,7 +60,7 @@ def test_text_widget():
     assert_equal(str(txt.text), 'goodbye, world!')
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_slider_int():
     viewer = get_image_viewer()
     sld = Slider('radius', 2, 10, value_type='int')
@@ -71,7 +74,7 @@ def test_slider_int():
     assert_equal(sld.val, 5)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_slider_float():
     viewer = get_image_viewer()
     sld = Slider('alpha', 2.1, 3.1, value=2.1, value_type='float',
@@ -86,7 +89,7 @@ def test_slider_float():
     assert_almost_equal(sld.val, 2.5, 2)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_save_buttons():
     viewer = get_image_viewer()
     sv = SaveButtons()
@@ -114,7 +117,7 @@ def test_save_buttons():
     os.remove(filename)
 
 
-@skipif(not viewer_available)
+@skipif(ImageViewer is None)
 def test_ok_buttons():
     viewer = get_image_viewer()
     ok = OKCancelButtons()
diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index 242f2de4..dd81d2a7 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -1,28 +1,17 @@
 import warnings
 
 import numpy as np
+from skimage.viewer.qt import QtGui
+import matplotlib as mpl
+from matplotlib.figure import Figure
+from matplotlib import _pylab_helpers
+from matplotlib.colors import LinearSegmentedColormap
 
-from ..qt import qt_api
-
-try:
-    import matplotlib as mpl
-    from matplotlib.figure import Figure
-    from matplotlib import _pylab_helpers
-    from matplotlib.colors import LinearSegmentedColormap
-    if not qt_api is None:
-        from matplotlib.backends.backend_qt4 import FigureManagerQT
-        from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
-        if 'agg' not in mpl.get_backend().lower():
-            print("Recommended matplotlib backend is `Agg` for full "
-                  "skimage.viewer functionality.")
-    else:
-        FigureCanvasQTAgg = object
-        LinearSegmentedColormap = object
-except ImportError:
-    FigureCanvasQTAgg = object  # hack to prevent nosetest and autodoc errors
-    LinearSegmentedColormap = object
-
-from ..qt import QtGui
+from matplotlib.backends.backend_qt4 import FigureManagerQT
+from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
+if 'agg' not in mpl.get_backend().lower():
+    warnings.warn("Recommended matplotlib backend is `Agg` for full "
+          "skimage.viewer functionality.")
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',
diff --git a/skimage/viewer/utils/dialogs.py b/skimage/viewer/utils/dialogs.py
index f160531d..20dd0e16 100644
--- a/skimage/viewer/utils/dialogs.py
+++ b/skimage/viewer/utils/dialogs.py
@@ -1,6 +1,6 @@
 import os
 
-from ..qt import QtGui
+from skimage.viewer.qt import QtGui
 
 
 __all__ = ['open_file_dialog', 'save_file_dialog']
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index 36ba6ee6..19112dc1 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -1,21 +1,15 @@
 """
 ImageViewer class for viewing and interacting with images.
 """
-from ..qt import QtGui, qt_api
-from ..qt.QtCore import Qt, Signal
-
-if qt_api is not None:
-    has_qt = True
-else:
-    has_qt = False
 
+from skimage.viewer.qt import QtWidgets, Qt, Signal
 from skimage import io, img_as_float
 from skimage.util.dtype import dtype_range
 from skimage.exposure import rescale_intensity
 import numpy as np
-from .. import utils
 from ..widgets import Slider
-from ..utils import dialogs
+from ..utils import (
+    dialogs, init_qtapp, figimage, start_qtapp, update_axes_image)
 from ..plugins.base import Plugin
 
 
@@ -152,7 +146,7 @@ class EventManager(object):
             tool.on_scroll(event)
 
 
-class ImageViewer(QtGui.QMainWindow):
+class ImageViewer(QtWidgets.QMainWindow):
     """Viewer for displaying images.
 
     This viewer is a simple container object that holds a Matplotlib axes
@@ -194,7 +188,7 @@ class ImageViewer(QtGui.QMainWindow):
 
     def __init__(self, image, useblit=True):
         # Start main loop
-        utils.init_qtapp()
+        init_qtapp()
         super(ImageViewer, self).__init__()
 
         #TODO: Add ImageViewer to skimage.io window manager
@@ -202,7 +196,7 @@ class ImageViewer(QtGui.QMainWindow):
         self.setAttribute(Qt.WA_DeleteOnClose)
         self.setWindowTitle("Image Viewer")
 
-        self.file_menu = QtGui.QMenu('&File', self)
+        self.file_menu = QtWidgets.QMenu('&File', self)
         self.file_menu.addAction('Open file', self.open_file,
                                  Qt.CTRL + Qt.Key_O)
         self.file_menu.addAction('Save to file', self.save_to_file,
@@ -211,7 +205,7 @@ class ImageViewer(QtGui.QMainWindow):
                                  Qt.CTRL + Qt.Key_Q)
         self.menuBar().addMenu(self.file_menu)
 
-        self.main_widget = QtGui.QWidget()
+        self.main_widget = QtWidgets.QWidget()
         self.setCentralWidget(self.main_widget)
 
         if isinstance(image, Plugin):
@@ -221,7 +215,7 @@ class ImageViewer(QtGui.QMainWindow):
             # When plugin is started, start
             plugin._started.connect(self._show)
 
-        self.fig, self.ax = utils.figimage(image)
+        self.fig, self.ax = figimage(image)
         self.canvas = self.fig.canvas
         self.canvas.setParent(self)
         self.ax.autoscale(enable=False)
@@ -236,7 +230,7 @@ class ImageViewer(QtGui.QMainWindow):
         self._update_original_image(image)
         self.plugins = []
 
-        self.layout = QtGui.QVBoxLayout(self.main_widget)
+        self.layout = QtWidgets.QVBoxLayout(self.main_widget)
         self.layout.addWidget(self.canvas)
 
         status_bar = self.statusBar()
@@ -255,7 +249,7 @@ class ImageViewer(QtGui.QMainWindow):
         if plugin.dock:
             location = self.dock_areas[plugin.dock]
             dock_location = Qt.DockWidgetArea(location)
-            dock = QtGui.QDockWidget()
+            dock = QtWidgets.QDockWidget()
             dock.setWidget(plugin)
             dock.setWindowTitle(plugin.name)
             self.addDockWidget(dock_location, dock)
@@ -341,7 +335,7 @@ class ImageViewer(QtGui.QMainWindow):
         """
         self._show()
         if main_window:
-            utils.start_qtapp()
+            start_qtapp()
         return [p.output() for p in self.plugins]
 
     def redraw(self):
@@ -357,7 +351,7 @@ class ImageViewer(QtGui.QMainWindow):
     @image.setter
     def image(self, image):
         self._img = image
-        utils.update_axes_image(self._image_plot, image)
+        update_axes_image(self._image_plot, image)
 
         # update display (otherwise image doesn't fill the canvas)
         h, w = image.shape[:2]
@@ -487,7 +481,7 @@ class CollectionViewer(ImageViewer):
         self._update_original_image(image)
 
     def keyPressEvent(self, event):
-        if type(event) == QtGui.QKeyEvent:
+        if type(event) == QtWidgets.QKeyEvent:
             key = event.key()
             # Number keys (code: 0 = key 48, 9 = key 57) move to deciles
             if 48 <= key < 58:
diff --git a/skimage/viewer/widgets/core.py b/skimage/viewer/widgets/core.py
index 4da8925b..ae8be4e7 100644
--- a/skimage/viewer/widgets/core.py
+++ b/skimage/viewer/widgets/core.py
@@ -15,17 +15,15 @@ parameter type specified by its `ptype` attribute, which can be:
         property of the same name that updates the display.
 
 """
-from ..qt import QtGui
-from ..qt import QtCore
-from ..qt.QtCore import Qt
-
+from ..qt import QtWidgets, QtCore, Qt
 from ..utils import RequiredAttr
 
 
 __all__ = ['BaseWidget', 'Slider', 'ComboBox', 'CheckBox', 'Text']
 
 
-class BaseWidget(QtGui.QWidget):
+
+class BaseWidget(QtWidgets.QWidget):
 
     plugin = RequiredAttr("Widget is not attached to a Plugin.")
 
@@ -49,11 +47,11 @@ class Text(BaseWidget):
 
     def __init__(self, name=None, text=''):
         super(Text, self).__init__(name)
-        self._label = QtGui.QLabel()
+        self._label = QtWidgets.QLabel()
         self.text = text
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         if name is not None:
-            name_label = QtGui.QLabel()
+            name_label = QtWidgets.QLabel()
             name_label.setText(name)
             self.layout.addWidget(name_label)
         self.layout.addWidget(self._label)
@@ -105,17 +103,17 @@ class Slider(BaseWidget):
         # Set widget orientation
         #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         if orientation == 'vertical':
-            self.slider = QtGui.QSlider(Qt.Vertical)
+            self.slider = QtWidgets.QSlider(Qt.Vertical)
             alignment = QtCore.Qt.AlignHCenter
             align_text = QtCore.Qt.AlignHCenter
             align_value = QtCore.Qt.AlignHCenter
-            self.layout = QtGui.QVBoxLayout(self)
+            self.layout = QtWidgets.QVBoxLayout(self)
         elif orientation == 'horizontal':
-            self.slider = QtGui.QSlider(Qt.Horizontal)
+            self.slider = QtWidgets.QSlider(Qt.Horizontal)
             alignment = QtCore.Qt.AlignVCenter
             align_text = QtCore.Qt.AlignLeft
             align_value = QtCore.Qt.AlignRight
-            self.layout = QtGui.QHBoxLayout(self)
+            self.layout = QtWidgets.QHBoxLayout(self)
         else:
             msg = "Unexpected value %s for 'orientation'"
             raise ValueError(msg % orientation)
@@ -151,11 +149,11 @@ class Slider(BaseWidget):
             raise ValueError("Unexpected value %s for 'update_on'" % update_on)
         self.slider.setFocusPolicy(QtCore.Qt.StrongFocus)
 
-        self.name_label = QtGui.QLabel()
+        self.name_label = QtWidgets.QLabel()
         self.name_label.setText(self.name)
         self.name_label.setAlignment(align_text)
 
-        self.editbox = QtGui.QLineEdit()
+        self.editbox = QtWidgets.QLineEdit()
         self.editbox.setMaximumWidth(max_edit_width)
         self.editbox.setText(self.value_fmt % self.val)
         self.editbox.setAlignment(align_value)
@@ -229,20 +227,18 @@ class ComboBox(BaseWidget):
     def __init__(self, name, items, ptype='kwarg', callback=None):
         super(ComboBox, self).__init__(name, ptype, callback)
 
-        self.name_label = QtGui.QLabel()
+        self.name_label = QtWidgets.QLabel()
         self.name_label.setText(self.name)
         self.name_label.setAlignment(QtCore.Qt.AlignLeft)
 
-        self._combo_box = QtGui.QComboBox()
+        self._combo_box = QtWidgets.QComboBox()
         self._combo_box.addItems(list(items))
 
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         self.layout.addWidget(self.name_label)
         self.layout.addWidget(self._combo_box)
 
         self._combo_box.currentIndexChanged.connect(self._value_changed)
-        # self.connect(self._combo_box,
-                # SIGNAL("currentIndexChanged(int)"), self.updateUi)
 
     @property
     def val(self):
@@ -283,11 +279,11 @@ class CheckBox(BaseWidget):
                  callback=None):
         super(CheckBox, self).__init__(name, ptype, callback)
 
-        self._check_box = QtGui.QCheckBox()
+        self._check_box = QtWidgets.QCheckBox()
         self._check_box.setChecked(value)
         self._check_box.setText(self.name)
 
-        self.layout = QtGui.QHBoxLayout(self)
+        self.layout = QtWidgets.QHBoxLayout(self)
         if alignment == 'center':
             self.layout.setAlignment(QtCore.Qt.AlignCenter)
         elif alignment == 'left':
diff --git a/skimage/viewer/widgets/history.py b/skimage/viewer/widgets/history.py
index d1df8689..ba0f0cd3 100644
--- a/skimage/viewer/widgets/history.py
+++ b/skimage/viewer/widgets/history.py
@@ -1,8 +1,6 @@
 from textwrap import dedent
 
-from ..qt import QtGui
-from ..qt import QtCore
-
+from ..qt import QtGui, QtCore
 import numpy as np
 
 import skimage