How to reduce/remove PNG anti-aliasing?

[jotto]

I'm not sure if this "anti-aliasing" or PNG compression or something else:

source:

sparklinesChart := chart.Chart{
  Width:  700,
  Height: 100,
  Series: []chart.Series{
    chart.ContinuousSeries{
      Style: chart.Style{
        Show: true,
        StrokeWidth: 5,
      },
      YValues: []float64{1,3,4,5,4,3,1,6},
      XValues: []float64{1,2,3,4,5,6,7,8},
    },
  },
}

buf := new(bytes.Buffer)
err := sparklinesChart.Render(chart.PNG, buf)

[carbocation]

I have the same issue and question.