Issue
Following the official example from the docs I can successfully create an altair scatter plot with each point having a tooltip:
import altair as alt
import pandas as pd
source = pd.DataFrame.from_records(
[{'a': 1, 'b': 1, 'image': 'https://altair-viz.github.io/_static/altair-logo-light.png'},
{'a': 2, 'b': 2, 'image': 'https://avatars.githubusercontent.com/u/11796929?s=200&v=4'}]
)
alt.Chart(source).mark_circle(size=200).encode(
x='a',
y='b',
tooltip=['image'] # Must be a list for the image to render
)
The result will look as follows
However I want to use a local image which I loaded via PIL. If i just replace the URL-string with the PIL object in the tooltip I get the error: TypeError: Object of type 'Image' is not JSON serializable
.
I then tried to convert to image to JSON following this SO answer
My code now looks as follows:
import json
from io import BytesIO
import base64
def image_formatter2(im):
with BytesIO() as buffer:
im.save(buffer, 'png')
data = base64.encodebytes(buffer.getvalue()).decode('utf-8')
return json.dumps(data)
temp = some_local_PIL_image.thumbnail((90,90))
source = pd.DataFrame.from_records(
[{'a': 1, 'b': 1, 'image': image_formatter2(temp)},
{'a': 2, 'b': 2, 'image': 'https://avatars.githubusercontent.com/u/11796929?s=200&v=4'}]
)
alt.Chart(source).mark_circle(size=200).encode(
x='a',
y='b',
tooltip=['image'] # Must be a list for the image to render
)
My tooltip is now empty! How can I display the local image in the tooltip?
Version info
IPython : 7.16.1
jupyter_client : 7.0.6
jupyter_core : 4.8.1
altair : 4.1.0
Solution
Ok I kind of figured it out. One has to add a prefix data:image/png;base64,
to the data. The code is now as follows:
import PIL.Image
from io import BytesIO
import base64
import json
def image_formatter2(im):
with BytesIO() as buffer:
im.save(buffer, 'png')
data = base64.encodebytes(buffer.getvalue()).decode('utf-8')
return f"data:image/png;base64,{data}" # <--------- this prefix is crucial
temp = some_local_PIL_image.thumbnail((90,90))
source = pd.DataFrame.from_records(
[{'a': 1, 'b': 1, 'image': image_formatter2(temp)},
{'a': 2, 'b': 2, 'image': 'https://avatars.githubusercontent.com/u/11796929?s=200&v=4'}]
)
alt.Chart(source).mark_circle(size=200).encode(
x='a',
y='b',
tooltip=['image'] # Must be a list for the image to render
)
Result
Since I didn't know the term/syntax and this may help others as well:
The term one has to look for is Data URLs
. Here is a nice intro: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
Answered By - v.tralala
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