How to plot smoother curves in R

Question

Using R , I have drawn a hatched plot. If you see the curves, they are not smooth. How to make them smooth ? Even excel plots far more smoother curves. Device features: windows 7, screen resolution=1366 x 768 (max)

Here is the plot.

plot

Following code is used to draw the plot.

plot(NA,xlim=c(0,1),ylim=c(0,1),xlab="delta",ylab="K", xaxs="i",yaxs="i") # Empty plot
a1 <- curve((x+x^7-x^2-x^4)/(1+x-x^3-x^4), from=0, n=450000, add = TRUE) # First curve

Full code is available here

You should also add the corresponding plot ..not the original one... — agstudy, Mar 16 '13 at 10:12
On what device (quartz/x11, jpeg/png/pdf...) did you plot it? — plannapus, Mar 16 '13 at 10:15
@AshniGoyal how did you produced the image file of the plot if you prefer, using functions `jpeg`, `png`.... or by just taking a screenshot of the plot window, or by using the save option of the GUI? — plannapus, Mar 16 '13 at 10:22
@plannapus right click on the plot, copy as bitmap , paste in paint, save. — Ashni Goyal, Mar 16 '13 at 10:24
@AshniGoyal you might benefit from reading tutorials or help file on how to save plots to file programmatically: it will allow you to keep a tighter control on the image quality than with the method you're using now. — plannapus, Mar 16 '13 at 10:32

score 9 · Answer 1 · answered Mar 16 '13 at 11:17

At the moment, it looks like your plot is jagged not because of the curve itself, but because of how your screen displays it.

@Hemmo proposed to fix this solution by using a vector graphics format instead of a raster format. This is the best solution, but if you desperately need to use a raster format, you can use anti-aliasing.

Anti-aliasing means that the plot is drawn with some grey fuzz around the lines so they look like they're curved to the human eye. You'll see this easily if you zoom in on an anti-aliased image. For now:

png("no-alias.png")
# Your code
dev.off()

enter image description here

cairographics offers anti-aliasing. So using it as an option to png:

png("alias.png", type="cairo")
# Your code again
dev.off()

enter image description here

Much appreciated on this one. Thanks. – Balter Mar 22 '17 at 20:31 — Balter, Mar 22 '17 at 20:31

Jouni Helske · Accepted Answer · 2013-03-16T10:30:10.410

I'm fairly certain that if you plot your figure for example as pdf, the curves are completely smooth. It's the Rgui's internal display which shows the curve as non-smooth, and using copy paste on that might cause problems. It's better to directly plot into the file, like this:

# Open device:
pdf("D:/test.pdf") #change for appropriate file path
plot(NA,xlim=c(0,1),ylim=c(0,1),xlab="delta",ylab="K", xaxs="i",yaxs="i")
a1 <- curve((x+x^7-x^2-x^4)/(1+x-x^3-x^4), from=0, n=450000, add = TRUE)
dev.off() #close device

Now look at the pdf, and it looks completely fine. If you want for example jpg image, use function jpeg etc, see ?jpeg for more details how to save as tiff, jpeg, png or bmp, and arguments for image size, resolution and such.

(note, the terms device etc used here might not be totally correct, I'm not completely familiar with this terminology, someone more clever can edit if appropriate).

I tried this method. `pdf` really works well, but using `png` does make any difference. — Ashni Goyal, Mar 16 '13 at 11:03
You don't need to close R? If you mean the dev.off line, that closes the pdf file from further writing. — Jouni Helske, Mar 16 '13 at 14:23

score 2 · Answer 3 · answered Mar 16 '13 at 10:40

I am not sure of your problem somthness(it is not clear in the plot you show), but you can ameliorate by doing cubic (or Hermite) spline interpolation of your points. Here some options using spline and splinefun.

enter image description here

layout(matrix(c(1,2,3),nrow=3,byrow=TRUE))
plot(NA,xlim=c(0,1),ylim=c(0,0.2),xlab="delta",ylab="K", xaxs="i",yaxs="i",
     main='orginal plot with 45000 points') # Empty plot
a1 <- curve((x+x^7-x^2-x^4)/(1+x-x^3-x^4), from=0, n=45000, add = TRUE)
x <- seq(0,1,length.out=1000)
y <- (x+x^7-x^2-x^4)/(1+x-x^3-x^4)
f <- splinefun(x, y)
plot(NA,xlim=c(0,1),ylim=c(0,0.2),xlab="delta",ylab="K", xaxs="i",yaxs="i",
     main='splinefun plot with 1000 points') 
curve(f(x),0, 1, col = "green", lwd = 1.5,add=TRUE)
plot(NA,xlim=c(0,1),ylim=c(0,0.2),xlab="delta",ylab="K", xaxs="i",yaxs="i",
     main='spline plot with 1000 points') 
lines(spline(x,y), col = 2)

How to plot smoother curves in R

3 Answers3

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