ENH: Set the alpha value for plots in rcParams

[Jul3k]

Using Matplotlib i often find myself repeadily writing the following to change the alpha value of the plots:

plot(x,y1, alpha=.6)
plot(x,y2, alpha=.6)
plot(x,y3, alpha=.6)
...

I was hoping to find a matching value in the rcParameters to change to option globally like:

plt.rcParams['lines.alpha'] = 0.6

Could this be implemented so it can be set in a style sheet and the code stays short and readable?

[tacaswell]

You can do this by setting a the color/prop cycle to use colors which have an alpha component.

The traitlet overhaul will take care of this as well

[Jul3k]

Can i set the "axes.color_cycle" values in hex natation as e.g.:
"#ff0000b4"
Because when i try to do so i receive an exception of "invalid hex color string"

[WeatherGod]

take out the pound sign because our rcfile reader is really naive and
always treats that as a comment symbol.

Also note that color_cycle is deprecated in the upcoming 1.5 release,
replaced with the more versatile "prop_cycle" mechanism. However, it will
likely be awhile before we actually remove "color_cycle".

On Thu, Sep 24, 2015 at 9:30 AM, Jul3k notifications@github.com wrote:

Can i set the "axes.color_cycle" values in hex natation as e.g.:
"#ff0000b4"
Because when i try to do so i receive an exception of "invalid hex color
string"

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#5132 (comment)
.

[Jul3k]

Without the pound sign i get a "to_rgb: Invalid rgb arg "ff0000b4"" error.
The exact call is:

plt.rcParams['axes.color_cycle'][0] = "ff0000b4"

matplotlib version 1.4.3

Without the alpha content ("b4") it works fine. It seams to me that the parser doese not accept 4 Byte hex color codes with alpha content. I could work around this by using the to_rgba builtin method

My workaround looks as follows:

to_rgba = matplotlib.colors.ColorConverter().to_rgba
for i, c in enumerate(plt.rcParams['axes.color_cycle']):
    plt.rcParams['axes.color_cycle'][i] = to_rgba(c,0.2)

[WeatherGod]

Ah, indeed, our hex color spec parser is just rgb, not rgb[a]. Sounds like
an easy feature to implement, though...

On Thu, Sep 24, 2015 at 10:21 AM, Jul3k notifications@github.com wrote:

Without the pound sign i get a "to_rgb: Invalid rgb arg "ff0000b4"" error.
The exact call is:
plt.rcParams['axes.color_cycle'][0] = "ff0000b4"

matplotlib version 1.4.3

Without the alpha content ("b4") it works fine. It seams to me that the
parser doese not accept 4 Byte hex color codes with alpha content. I could
work around this by using the to_rgba builtin method

My working code looks as follows:
to_rgba = matplotlib.colors.ColorConverter().to_rgba
for i, c in enumerate(plt.rcParams['axes.color_cycle']):
plt.rcParams['axes.color_cycle'][i] = to_rgba(c,0.2)

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#5132 (comment)
.

[tacaswell]

Pretty sure rcparams will take a 4-tuple an input

[Jul3k]

Yes rcparams takes a 4-tuple as an input. As @WeatherGod stated the problem was related to the fact that the color parser only checks for 3-Byte (#FFFFFF) color strings and does not understand 4-Byte (#FFFFFFAA) color strings with alpha channel. So the way i presented the color information was not suiteable to the parser

[tacaswell]

@Jul3k Can you make a new issue to upgrade out hex parser to deal with RGBA hex codes?

[Jul3k]

I opend a new issue relating to the color spec parser

[WeatherGod]

I think this is closed by #6382, which updated the parser to allow 4-byte hex strings. Re-open this issue if that isn't sufficient.

[JoElfner]

I frequently need alpha independently of the color cycler. Most importantly I want different plots to have different default alphas, f.i. alpha=.5 for my scatter plots, while not using alpha for my line plots. Thus, as far as I can see, setting alpha to the color cycle is not working. Any change this is going to be implemented in the rcParams?

[timhoffm]

This is too specialized for rcParams, in particular if you want to have different values for scatter plots and line plots.