class_docstr: :class:`~pyqtgraph.GraphicsWidget` with controls for adjusting the display of an
  :class:`~pyqtgraph.ImageItem`.
  
  Includes:
  
    - Image histogram
    - Movable region over the histogram to select black/white levels
    - Gradient editor to define color lookup table for single-channel images
  
  Parameters
  ----------
  image : pyqtgraph.ImageItem, optional
      If provided, control will be automatically linked to the image and changes to
      the control will be reflected in the image's appearance. This may also be set
      via :meth:`setImageItem`.
  fillHistogram : bool, optional
      By default, the histogram is rendered with a fill. Performance may be improved
      by disabling the fill. Additional control over the fill is provided by
      :meth:`fillHistogram`.
  levelMode : str, optional
      'mono' (default)
          One histogram with a :class:`~pyqtgraph.LinearRegionItem` is displayed to
          control the black/white levels of the image. This option may be used for
          color images, in which case the histogram and levels correspond to all
          channels of the image.
      'rgba'
          A histogram and level control pair is provided for each image channel. The
          alpha channel histogram and level control are only shown if the image
          contains an alpha channel.
  gradientPosition : str, optional
      Position of the gradient editor relative to the histogram. Must be one of
      {'right', 'left', 'top', 'bottom'}. 'right' and 'left' options should be used
      with a 'vertical' orientation; 'top' and 'bottom' options are for 'horizontal'
      orientation.
  orientation : str, optional
      The orientation of the axis along which the histogram is displayed. Either
      'vertical' (default) or 'horizontal'.
  
  Attributes
  ----------
  sigLookupTableChanged : QtCore.Signal
      Emits the HistogramLUTItem itself when the gradient changes
  sigLevelsChanged : QtCore.Signal
      Emits the HistogramLUTItem itself while the movable region is changing
  sigLevelChangeFinished : QtCore.Signal
      Emits the HistogramLUTItem itself when the movable region is finished changing
  
  See Also
  --------
  :class:`~pyqtgraph.ImageItem`
      HistogramLUTItem is most useful when paired with an ImageItem.
  :class:`~pyqtgraph.ImageView`
      Widget containing a paired ImageItem and HistogramLUTItem.
  :class:`~pyqtgraph.HistogramLUTWidget`
      QWidget containing a HistogramLUTItem for widget-based layouts.
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code: def regionChanged(self):
      if self.imageItem() is not None:
          self.imageItem().setLevels(self.getLevels())
      self.sigLevelChangeFinished.emit(self)
  
imports: import weakref
  import numpy
  from ..None import debug
  from ..None import functions
  from ..Point import Point
  from ..Qt import QtCore, QtGui, QtWidgets
  from .AxisItem import AxisItem
  from .GradientEditorItem import GradientEditorItem
  from .GraphicsWidget import GraphicsWidget
  from .LinearRegionItem import LinearRegionItem
  from .PlotCurveItem import PlotCurveItem
  from .ViewBox import ViewBox
label_desc: Use image node_id 13 for calling the HistogramLUTItem obj's underlying member method code with example usage: obj.regionChanged() without return types