title: scatter plot with single pixel marker in matplotlib
body: <p>I am trying to plot a large dataset with a scatter plot. 
  I want to use matplotlib to plot it with single pixel marker. 
  It seems to have been solved.</p>
  
  <p><a href="https://github.com/matplotlib/matplotlib/pull/695" rel="noreferrer">https://github.com/matplotlib/matplotlib/pull/695</a></p>
  
  <p>But I cannot find a mention of how to get a single pixel marker. </p>
  
  <p>My simplified dataset (data.csv)</p>
  
  <pre><code>Length,Time
  78154393,139.324091
  84016477,229.159305
  84626159,219.727537
  102021548,225.222662
  106399706,221.022827
  107945741,206.760239
  109741689,200.153263
  126270147,220.102802
  207813132,181.67058
  610704756,50.59529
  623110004,50.533158
  653383018,52.993885
  659376270,53.536834
  680682368,55.97628
  717978082,59.043843
  </code></pre>
  
  <p>My code is below.</p>
  
  <pre><code>import pandas as pd
  import os
  import numpy
  import matplotlib.pyplot as plt
  
  inputfile='data.csv'
  iplevel = pd.read_csv(inputfile)
  base = os.path.splitext(inputfile)[0]
  
  fig = plt.figure()
  plt.yscale('log')
  #plt.xscale('log')
  plt.title(' My plot:  '+base)
  plt.xlabel('x')
  plt.ylabel('y')
  plt.scatter(iplevel['Time'], iplevel['Length'],color='black',marker=',',lw=0,s=1)
  fig.tight_layout()
  fig.savefig(base+'_plot.png', dpi=fig.dpi)
  </code></pre>
  
  <p>You can see below that the points are not single pixel. </p>
  
  <p><a href="https://i.stack.imgur.com/Z6sB6.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Z6sB6.png" alt="data_plot.png"></a></p>
  
  <p>Any help is appreciated</p>