现在遇到使用R图，需要变成.tiff格式，并且要求：
1） Figures that fit exactly the width of 1 column (72 mm) or 2 columns (148 mm) expedite the publication process.
2）1200 DPI/PPI for monochrome (black and white line art).
This resolution applies to images that are purely black and white. Images such as line graphs or diagrams fall in this category. If your image editing program allows it, LZW file compression can be used on a monochrome image to greatly reduce its file size.

现在假设c是自变量一组值，而pvalue是因变量亦是一组值，画它们的平面图：
tiff(file="Fig.3.tif")
plot(c,pvalue,type="l",xlab=("C"),ylab=c("P-Value"))
abline(h=0.05)
abline(v=shang,lty=2)
dev.off()

怎么实现上边的两点要求呢？即1200 DPI/PPI；72mm宽呢？