[R] Artifacts in pdf() of image() (w/o comments)

[Michael Kubovy]

On Aug 12, 2007, at 6:24 AM, Duncan Murdoch wrote:

> Michael Kubovy wrote:
>> Dear r-helpers,
>>
>> In my previous message there were comments in the code that may  
>> have  made cutting and pasting awkward. Here it is w/o them.
>>
>> I have two questions:
>>
>> (1) The following produces a pdf with artifacts. How do I prevent  
>> them?
>>
>
> What artifacts do you see?  It looks like a smoothly varying field  
> when produced by R 2.5.1 and viewed in Acrobat Reader 6.0 on Windows.
>
> Duncan Murdoch
>> require(grDevices)
>> imSize <- 200
>> lambda <- 10
>> theta <- 15
>> sigma <- 40
>> x <- 1:imSize
>> x0 <- x / imSize -.5
>> freq = imSize/lambda
>> xf = x0 * freq * 2 * pi
>> f <- function(x, y){r <- -((x^2 + y^2)/(sigma ^2)); exp(r)}
>> z <- outer(xf, xf, f)
>> f1 <- function(x, y){cos(.1 * x)}
>> z1 <- outer(xf, xf, f1)
>> pdf('gabor.pdf')
>> image(xf, xf, z * z1, col = gray(250:1000/1000),
>> xlab = '', ylab =  '', bty = 'n', axes = FALSE, asp = 1)
>> dev.off()

I'm working on a Mac. You're right, Acrobat 6.05 renders the figure  
nicely, but when it's included in a LaTeX-produced pdf or viewed with  
the Mac Preview program, a grid of fine white lines is superimposed  
on the figure. So I believe that it's a matter of aliasing, which I  
might be able to prevent by adjusting the parameters of the figures.  
I just don't know enough to figure this out, and would appreciate  
guidance.

_____________________________
Professor Michael Kubovy
University of Virginia
Department of Psychology
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