Severe image quality degradation when using put_image_data

[snydej]

Using put_image_data to draw to the canvas results in what looks like very pronounced compression artifacts and a substantial loss of detail as shown below (open image in a new tab to be sure to see the full detail present in the second image):

The second image was produced by the pillow library and authentically represents the image data. The relevant drawing code for the first image is this:

    def render_fractal(self):
        evalresult = evaluate_mandelbrot(self.view, 1e6, 1000)
        self.img_data = to_image_array(evalresult, rainbow_colormap)
        self.canvases[0].put_image_data(self.img_data)