Matplotlib graphic image to base64

Question

Problem : Need to transform a graphic image of matplotlib to a base64 image

Current Solution : Save the matplot image in a cache folder and read it with read() method and then convert to base64

New Problem : Annoyance : Need a workaround so I dont need to save the graphic as image in any folder. I want to just use the image in the memory. Doing unnecessary I/O is a bad practice.

def save_single_graphic_data(data, y_label="Loss", x_label="Epochs", save_as="data.png"):
    total_epochs = len(data)
    plt.figure()
    plt.clf()

    plt.plot(total_epochs, data)

    ax = plt.gca()
    ax.ticklabel_format(useOffset=False)

    plt.ylabel(y_label)
    plt.xlabel(x_label)

    if save_as is not None:
        plt.savefig(save_as)

    plt.savefig("cache/cached1.png")

    cached_img = open("cache/cached1.png")

    cached_img_b64 = base64.b64encode(cached_img.read())

    os.remove("cache/cached1.png")

    return cached_img_b64

Joran Beasley · Accepted Answer · 2023-02-01 18:20:53Z

46

import cStringIO
my_stringIObytes = cStringIO.StringIO()
plt.savefig(my_stringIObytes, format='jpg')
my_stringIObytes.seek(0)
my_base64_jpgData = base64.b64encode(my_stringIObytes.read())

[edit] in python3 it should be

import io
my_stringIObytes = io.BytesIO()
plt.savefig(my_stringIObytes, format='jpg')
my_stringIObytes.seek(0)
my_base64_jpgData = base64.b64encode(my_stringIObytes.read()).decode()

I think at least ... based on the documentation http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.savefig

edited Feb 1, 2023 at 18:20

answered Jun 27, 2016 at 19:04

Joran Beasley

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7 Comments

Raniere Silva Over a year ago

If you are using Python 3 or greater, you need to use io.BytesIO as mentioned by @nobar at stackoverflow.com/a/18284900/1802726.

A T Over a year ago

Or for Python 2/3 compatibility with fastest implementation: try: from cStringIO import StringIO; except ImportError: from six import StringIO (six ref)

roudan Over a year ago

Hi Joran, from your code, where is the figure variable? I only see my_stringIObytes, I don't see any variable related to original mtaplotlib plot object. Thanks for clarifying.

Joran Beasley Over a year ago

my_base64_jpgData has the base64 encoded data you could then do something like <img src="data:image/jpeg;base64,{my_base64_jpgData}" /> or use other methods to decode it back to the original image

kn_pavan Over a year ago

my_base64_jpgData might have to be wrapped in an str(), as the data is in binary string format by default. ( b'sfsafs')

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BoyePanthera · Accepted Answer · 2019-12-19 17:21:04Z

27

For python 3

import base64
import io 
pic_IObytes = io.BytesIO()
plt.savefig(pic_IObytes,  format='png')
pic_IObytes.seek(0)
pic_hash = base64.b64encode(pic_IObytes.read())

The reason is both cStringIO and cStringIO.StringIO() are deprecated

answered Dec 19, 2019 at 17:21

BoyePanthera

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2 Comments

Yulia V Over a year ago

You might want to add a more detailed explanation

BoyePanthera Over a year ago

@YuliaV what I was saying is that in Python 3 the cStringIO module has been deprecated in place of io module. So that is why I used the io module in my answer.

Rex D · Accepted Answer · 2020-08-12 17:22:07Z

20

I could not get answers above work, but this did:

    import io
    import base64
    s = io.BytesIO()
    plt.plot(list(range(100)))
    plt.savefig(s, format='png', bbox_inches="tight")
    plt.close()
    s = base64.b64encode(s.getvalue()).decode("utf-8").replace("\n", "")
    return '<img align="left" src="data:image/png;base64,%s">' % s

answered Aug 12, 2020 at 17:22

Rex D

4973 silver badges9 bronze badges

1 Comment

Qbik Over a year ago

is it the fastest solution ?

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