如何在R中增加绘制区域字云的大小

http://onertipaday.blogspot.com/2011/07/word-cloud-in-r.html

需要帮助找出如何增加单词云的绘制面积.更改png(“wordcloud_packages.png”,width = 1280,height = 800)中的高度和宽度参数只会更改画布的高度和宽度,但绘制的区域仍然很小.

require(XML)
require(tm)
require(wordcloud)
require(RColorBrewer)
u = "http://cran.r-project.org/web/packages/available_packages_by_date.html"
t = readHTMLTable(u)[[1]]
ap.corpus <- Corpus(DataframeSource(data.frame(as.character(t[,3]))))
ap.corpus <- tm_map(ap.corpus,removePunctuation)
ap.corpus <- tm_map(ap.corpus,tolower)
ap.corpus <- tm_map(ap.corpus,function(x) removeWords(x,stopwords("english")))
ap.tdm <- TermDocumentMatrix(ap.corpus)
ap.m <- as.matrix(ap.tdm)
ap.v <- sort(rowSums(ap.m),decreasing=TRUE)
ap.d <- data.frame(word = names(ap.v),freq=ap.v)
table(ap.d$freq)
pal2 <- brewer.pal(8,"Dark2")
png("wordcloud_packages.png",width=1280,height=800)
wordcloud(ap.d$word,ap.d$freq,scale=c(8,.2),min.freq=3,max.words=Inf,random.order=FALSE,rot.per=.15,colors=pal2)
dev.off()