.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_gallery_user_interfaces_canvasagg.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_user_interfaces_canvasagg.py:


==============
CanvasAgg demo
==============

This example shows how to use the agg backend directly to create images, which
may be of use to web application developers who want full control over their
code without using the pyplot interface to manage figures, figure closing etc.

.. note::

    It is not necessary to avoid using the pyplot interface in order to
    create figures without a graphical front-end - simply setting
    the backend to "Agg" would be sufficient.

In this example, we show how to save the contents of the agg canvas to a file,
and how to extract them to a string, which can in turn be passed off to PIL or
put in a numpy array.  The latter functionality allows e.g. to use Matplotlib
inside a cgi-script *without* needing to write a figure to disk.



.. code-block:: python


    from matplotlib.backends.backend_agg import FigureCanvasAgg
    from matplotlib.figure import Figure
    import numpy as np

    fig = Figure(figsize=(5, 4), dpi=100)
    # A canvas must be manually attached to the figure (pyplot would automatically
    # do it).  This is done by instantiating the canvas with the figure as
    # argument.
    canvas = FigureCanvasAgg(fig)

    # Do some plotting.
    ax = fig.add_subplot(111)
    ax.plot([1, 2, 3])

    # Option 1: Save the figure to a file; can also be a file-like object (BytesIO,
    # etc.).
    fig.savefig("test.png")

    # Option 2: Save the figure to a string.
    canvas.draw()
    s, (width, height) = canvas.print_to_buffer()

    # Option 2a: Convert to a NumPy array.
    X = np.fromstring(s, np.uint8).reshape((height, width, 4))

    # Option 2b: Pass off to PIL.
    from PIL import Image
    im = Image.frombytes("RGBA", (width, height), s)

    # Uncomment this line to display the image using ImageMagick's `display` tool.
    # im.show()







------------

References
""""""""""

The use of the following functions, methods, classes and modules is shown
in this example:



.. code-block:: python


    import matplotlib
    matplotlib.backends.backend_agg.FigureCanvasAgg
    matplotlib.figure.Figure
    matplotlib.figure.Figure.add_subplot
    matplotlib.figure.Figure.savefig
    matplotlib.axes.Axes.plot







.. _sphx_glr_download_gallery_user_interfaces_canvasagg.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: canvasagg.py <canvasagg.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: canvasagg.ipynb <canvasagg.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    Keywords: matplotlib code example, codex, python plot, pyplot
    `Gallery generated by Sphinx-Gallery
    <https://sphinx-gallery.readthedocs.io>`_
