title: ggplot2 geom_line chart output quailty is poor. The time series lines look very fuzzy
body: <p>I have the following code snippet to produce a time series line charts for three time series":</p>
  
  <pre><code>ggplot() +
    #theme_light() +
    geom_line(data = Res,aes(x = as.Date(Res$Date), y = Res$AU, color = "AU"), lwd = 0.8) +
    geom_line(data = Res,aes(x = as.Date(Res$Date), y = Res$US, color = "US"), lwd = 0.8) + 
    geom_line(data = Res,aes(x = as.Date(Res$Date), y = Res$UK, color = "UK"), lwd = 0.8) +
    geom_point(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$AU, color = "AU"), size = 5,alpha = 0.5) +
    geom_point(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$US, color = "US"), size = 5,alpha = 0.5) +
    geom_point(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$UK, color = "UK"), size = 5,alpha = 0.5) +
    geom_text(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$AU,  color = "AU", label = currentDp$AU ), vjust = 2, size = 4) + 
    geom_text(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$US,  color = "US", label = currentDp$US ), vjust = 2, size = 4) + 
    geom_text(data = currentDp, aes(x = as.Date(currentDp$Date), y = currentDp$UK,  color = "UK", label = currentDp$UK ), vjust = 2, size = 4) + 
    scale_x_date(breaks = "8 weeks") + 
    ylab(label='') +
    xlab(label='Date') +
    labs(color="") +  
    #because the label is rotated it is the vertical space needs to be adjusted to align the text to the tick marks  
    theme(axis.text.x = element_text(angle = 90,vjust= 0.5)) +
    scale_colour_brewer(palette="Set1")
  </code></pre>
  
  <p>The Raw data frame looks like this (the currentDp data frame is just a slice of original frame containing the last entry of the time series in order to make annotation):</p>
  
  <pre><code>                  ![Date         AU          US        UK
  1  2014-01-02 15:27:00 -0.5829278  0.41575243 0.2067297
  2  2014-01-10 19:50:00 -0.6624452  0.45146732 0.1282591
  3  2014-01-17 07:58:00 -0.8211819  0.44135680 0.1635130
  4  2014-01-24 10:31:00 -0.7604532  0.40848431 0.2925148
  5  2014-01-31 09:42:00 -0.7680846  0.19470044 0.2533643
  6  2014-02-07 09:10:00 -0.8509427  0.15737371 0.3267309
  7  2014-02-14 09:13:00 -0.6053357  0.15124135 0.3884230
  8  2014-02-21 09:22:00 -0.7026988  0.10142252 0.3349704
  9  2014-02-28 08:47:00 -0.8186539  0.09725343 0.1194897
  10 2014-03-07 10:14:00 -0.4283892  0.06974185 0.1529529
  11 2014-03-14 08:13:00 -0.4626554  0.09613427 0.1409370
  12 2014-03-21 09:47:00 -0.4361898  0.10698534 0.1559909
  13 2014-03-28 09:16:00 -0.4361898  0.13999161 0.4359879
  14 2014-04-04 09:26:00 -0.5386579  0.16017797 0.4019338
  15 2014-04-11 08:52:00 -0.4187301  0.15845762 0.4302058]
  </code></pre>
  
  <p>However the ouput image quality looks really poor. I am using rstudio/R3.1.1 64 bit on a windows machine.</p>
  
  <p><img src="https://i.stack.imgur.com/Llyc1.jpg" alt="the output chart"></p>
  
  <p>The lines look like having uneven thichness and there are some clear zig-zag ness on a straight line. Is this normal? How can I improve the quality?</p>
  
  <p>The line chart samples i have seen on the web all have very smooth quality (even for line charts showing stock price)</p>
  
  <p>Thanks</p>
  
  <p>Casbby</p>
  
  <p><strong>Update</strong></p>
  
  <p>I am using the export option from the RStudio menu. I have yet to write the export code. I exported the image as jpg/png/bmp. All of them look having the same problem. SVG on the other hand does look a lot better. but I need use a batch program to produce powerpoint with the charts embeded hence i am not using SVG. </p>