import matplotlib.pyplot as plt size = 256,16 dpi = 72.0 figsize= size[0]/float(dpi),size[1]/float(dpi) fig = plt.figure(figsize=figsize, dpi=dpi) fig.patch.set_alpha(0) plt.axes([0,0.1,1,.8], frameon=False) for i in range(1,11): plt.axvline(i, linewidth=1, color='blue',alpha=.25+.75*i/10.) plt.xlim(0,11) plt.xticks([]), plt.yticks([]) plt.savefig('../figures/alpha.png', dpi=dpi)