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DOC: Clarify transparency in colors
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‎tutorials/colors/colors.py‎

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"""
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*****************
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Specifying Colors
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Specifying colors
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*****************
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Color formats
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=============
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Matplotlib recognizes the following formats to specify a color.
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+--------------------------------------+--------------------------------------+
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"Red", "Green", and "Blue" are the intensities of those colors. In combination,
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they represent the colorspace.
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Matplotlib draws Artists based on the ``zorder`` parameter. If there are no
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specified values, Matplotlib defaults to the order of the Artists added to the
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Axes.
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The alpha for an Artist controls opacity. It indicates how the RGB color of the
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new Artist combines with RGB colors already on the Axes.
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The two Artists combine with alpha compositing. Matplotlib uses the equation
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below to compute the result of blending a new Artist.
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Transparency
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============
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::
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The *alpha* value of a color specifies its transparency, where 0 is fully
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transparent and 1 is fully opaque. When a color is semi-transparent, the
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background color will show through (see also :doc:`/gallery/misc/zorder_demo`
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to learn more about the drawing order).
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RGB_{new} = RGB_{below} * (1 - \\alpha) + RGB_{artist} * \\alpha
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The *alpha* value determines the resulting color by blending the
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foreground color with the background color according to the formula
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Alpha of 1 indicates the new Artist completely covers the previous color.
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Alpha of 0 for top color is not visible; however, it contributes to blending
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for intermediate values as the cumulative result of all previous Artists. The
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following table contains examples.
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.. math::
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+---------------+-------------------------------------------------------------+
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| Alpha value | Visual |
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+===============+=============================================================+
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| ``0.3`` | .. image:: ../../_static/color_zorder_A.png |
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+---------------+-------------------------------------------------------------+
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| ``1`` | .. image:: ../../_static/color_zorder_B.png |
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+---------------+-------------------------------------------------------------+
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RGB_{result} = RGB_{background} * (1 - \\alpha) + RGB_{foreground} * \\alpha
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.. note::
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The following plot shows a semi-transparent (*alpha*=0.8) orange rectangle.
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The sequences of blue squares illustrate how different *alpha* values interact
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with the orange rectangle. The top row of blue squares is drawn below and the
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bottom row of blue squares is drawn on top of the orange rectangle.
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"""
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Changing the order of Artists will generally change the resulting figure.
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import matplotlib.pyplot as plt
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from matplotlib.patches import Rectangle
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import numpy as np
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fig, ax = plt.subplots(figsize=(6.5, 1.65), layout='constrained')
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ax.add_patch(Rectangle((-0.2, -0.35), 11.2, 0.7, color='C1', alpha=0.8))
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for i, alpha in enumerate(np.linspace(0, 1, 11)):
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ax.add_patch(Rectangle((i, 0.05), 0.8, 0.6, alpha=alpha, zorder=0))
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ax.text(i+0.4, 0.85, f"{alpha:.1f}", ha='center')
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ax.add_patch(Rectangle((i, -0.05), 0.8, -0.6, alpha=alpha, zorder=2))
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ax.set_xlim(-0.2, 13)
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ax.set_ylim(-1, 1)
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ax.set_title('alpha values')
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ax.text(11.3, 0.6, 'zorder=1', va='center', color='C0')
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ax.text(11.3, 0, 'zorder=2\nalpha=0.8', va='center', color='C1')
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ax.text(11.3, -0.6, 'zorder=3', va='center', color='C0')
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ax.axis('off')
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"CN" color selection
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--------------------
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Matplotlib converts "CN" colors to RGBA when drawing Artists. The
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:doc:`/tutorials/intermediate/color_cycle` section contains additional
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information about controlling colors and style properties.
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"""
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###############################################################################
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# "CN" color selection
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# ====================
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#
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# Matplotlib converts "CN" colors to RGBA when drawing Artists. The
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# :doc:`/tutorials/intermediate/color_cycle` section contains additional
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# information about controlling colors and style properties.
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import numpy as np
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# .. _xkcd-colors:
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#
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# Comparison between X11/CSS4 and xkcd colors
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# -------------------------------------------
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# ===========================================
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#
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# The xkcd colors come from a `user survey conducted by the webcomic xkcd
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# <https://blog.xkcd.com/2010/05/03/color-survey-results/>`__.

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