67 lines
2.8 KiB
ReStructuredText
67 lines
2.8 KiB
ReStructuredText
ImageItem
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=========
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:class:`~pyqtgraph.ImageItem` displays images inside a :class:`~pyqtgraph.GraphicsView`, or a
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:class:`~pyqtgraph.ViewBox`, which may itself be part of a :class:`~pyqtgraph.PlotItem`. It is designed
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for rapid updates as needed for a video display. The supplied data is optionally scaled (see
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:func:`~pyqtgraph.ImageItem.setLevels`) and/or colored according to a
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lookup table (see :func:`~pyqtgraph.ImageItem.setLookupTable`.
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Data is provided as a NumPy array with an ordering of either
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* `col-major`, where the shape of the array represents (width, height) or
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* `row-major`, where the shape of the array represents (height, width).
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While `col-major` is the default, `row-major` ordering typically has the best performance. In either ordering,
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a third dimension can be added to the array to hold individual
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``[R,G,B]`` or ``[R,G,B,A]`` components.
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Notes
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-----
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Data ordering can be set for each ImageItem, or in the :ref:`global configuration options <apiref_config>` by ::
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pyqtgraph.setConfigOption('imageAxisOrder', 'row-major') # best performance
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An image can be placed into a plot area of a given extent directly through the
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:func:`~pyqtgraph.ImageItem.setRect` method or the ``rect`` keyword. This is internally realized through
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assigning a ``QtGui.QTransform``. For other translation, scaling or rotations effects that
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persist for all later image data, the user can also directly define and assign such a
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transform, as shown in the example below.
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ImageItem is frequently used in conjunction with :class:`~pyqtgraph.ColorBarItem` to provide
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a color map display and interactive level adjustments, or with
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:class:`~pyqtgraph.HistogramLUTItem` or :class:`~pyqtgraph.HistogramLUTWidget` for a full GUI
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to control the levels and lookup table used to display the image.
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If performance is critial, the following points may be worth investigating:
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* Use row-major ordering and C-contiguous image data.
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* Manually provide ``level`` information to avoid autoLevels sampling of the image.
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* Prefer `float32` to `float64` for floating point data, avoid NaN values.
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* Use lookup tables with <= 256 entries for false color images.
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* Avoid individual level adjustments RGB components.
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* Use the latest version of NumPy. Notably, SIMD code added in version 1.20 significantly improved performance on Linux platforms.
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* Enable Numba with ``pyqtgraph.setConfigOption('useNumba', True)``, although the JIT compilation will only accelerate repeated image display.
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.. _ImageItem_examples:
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Examples
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--------
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.. literalinclude:: ../images/gen_example_imageitem_transform.py
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:lines: 19-28
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:dedent: 8
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.. image::
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../images/example_imageitem_transform.png
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:width: 49%
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:alt: Example of transformed image display
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.. autoclass:: pyqtgraph.ImageItem
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:members:
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.. automethod:: pyqtgraph.ImageItem.__init__
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