Matplotlib using image for points on plot

Question

I have the following matplotlib script. I want to replace the points on the plot with images. Let's say 'red.png' for the red points and 'blue.png' for the blue points. How can I adjust the following to plot these images instead of the default points?

from scipy import linalg
import numpy as np
import pylab as pl
import matplotlib as mpl
import matplotlib.image as image

from sklearn.qda import QDA

###############################################################################
# load sample dataset
from sklearn.datasets import load_iris

iris = load_iris()
X = iris.data[:, 0:2]  # Take only 2 dimensions
y = iris.target
X = X[y > 0]
y = y[y > 0]
y -= 1
target_names = iris.target_names[1:]

###############################################################################
# QDA
qda = QDA()
y_pred = qda.fit(X, y, store_covariances=True).predict(X)


###############################################################################
# Plot results

# constants
dpi = 72; imageSize = (32,32)
# read in our png file
im_red = image.imread('red.png')
im_blue = image.imread('blue.png')

def plot_ellipse(splot, mean, cov, color):
    v, w = linalg.eigh(cov)
    u = w[0] / linalg.norm(w[0])
    angle = np.arctan(u[1] / u[0])
    angle = 180 * angle / np.pi  # convert to degrees
    # filled gaussian at 2 standard deviation
    ell = mpl.patches.Ellipse(mean, 2 * v[0] ** 0.5, 2 * v[1] ** 0.5,
                                            180 + angle, color=color)
    ell.set_clip_box(splot.bbox)
    ell.set_alpha(0.5)
    splot.add_artist(ell)

xx, yy = np.meshgrid(np.linspace(4, 8.5, 200), np.linspace(1.5, 4.5, 200))
X_grid = np.c_[xx.ravel(), yy.ravel()]
zz_qda = qda.predict_proba(X_grid)[:, 1].reshape(xx.shape)

pl.figure()
splot = pl.subplot(1, 1, 1)
pl.contourf(xx, yy, zz_qda > 0.5, alpha=0.5)
pl.scatter(X[y == 0, 0], X[y == 0, 1], c='b', label=target_names[0])
pl.scatter(X[y == 1, 0], X[y == 1, 1], c='r', label=target_names[1])
pl.contour(xx, yy, zz_qda, [0.5], linewidths=2., colors='k')
print(xx)
pl.axis('tight')
pl.show()

forty_two · Accepted Answer · 2017-10-27 19:48:15Z

7

You can plot images instead of markers in a figure using BboxImage as in this tutorial.

from matplotlib import pyplot as plt
from matplotlib.image import BboxImage
from matplotlib.transforms import Bbox, TransformedBbox

# Load images.
redMarker = plt.imread('red.jpg')
blueMarker = plt.imread('blue.jpg')

# Data
blueX = [1, 2, 3, 4]
blueY = [1, 3, 5, 2]
redX = [1, 2, 3, 4]
redY = [3, 2, 3, 4]

# Create figure
fig = plt.figure()
ax = fig.add_subplot(111)

# Plots an image at each x and y location. 
def plotImage(xData, yData, im):
    for x, y in zip(xData, yData):
        bb = Bbox.from_bounds(x,y,1,1)  
        bb2 = TransformedBbox(bb,ax.transData)
        bbox_image = BboxImage(bb2,
                            norm = None,
                            origin=None,
                            clip_on=False)

        bbox_image.set_data(im)
        ax.add_artist(bbox_image)


plotImage(blueX, blueY, blueMarker)
plotImage(redX, redY, redMarker)

# Set the x and y limits
ax.set_ylim(0,6)
ax.set_xlim(0,6)

plt.show()

enter image description here

edited Oct 27, 2017 at 19:48

forty_two

5444 silver badges12 bronze badges

answered Aug 15, 2014 at 20:33

Molly

13.7k4 gold badges46 silver badges46 bronze badges

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2 Comments

Jeef Over a year ago

My image ended up in a strange skew :(

MLenthousiast Over a year ago

For others experiencing the image deformation, you can adjust the two 1's in this line bb = Bbox.from_bounds(x,y,1,1), for example to bb = Bbox.from_bounds(x,y,1,2) to make the images twice as high as they are wide.

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