python - Matplotlib figure to image as a numpy array

Question

I'm trying to get a numpy array image from a Matplotlib figure and I'm currently doing it by saving to a file, then reading the file back in, but I feel like there has to be a better way. Here's what I'm doing now:

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

fig = Figure()
canvas = FigureCanvas(fig)
ax = fig.gca()

ax.text(0.0,0.0,"Test", fontsize=45)
ax.axis('off')

canvas.print_figure("output.png")
image = plt.imread("output.png")

I tried this:

image = np.fromstring( canvas.tostring_rgb(), dtype='uint8' )

from an example I found but it gives me an error saying that 'FigureCanvasAgg' object has no attribute 'renderer'.

Answer 1

In order to get the figure contents as RGB pixel values, the matplotlib.backend_bases.Renderer needs to first draw the contents of the canvas. You can do this by manually calling canvas.draw():

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

fig = Figure()
canvas = FigureCanvas(fig)
ax = fig.gca()

ax.text(0.0,0.0,"Test", fontsize=45)
ax.axis('off')

canvas.draw()       # draw the canvas, cache the renderer

image = np.fromstring(canvas.tostring_rgb(), dtype='uint8')

See here for more info on the matplotlib API.