| png {grDevices} | R Documentation |
BMP, JPEG and PNG graphics devices
Description
A graphics device for BMP, JPEG or PNG format bitmap files.
Usage
bmp(filename = "Rplot%03d.bmp", width = 480, height = 480,
pointsize = 12, bg = "white", res = NA)
jpeg(filename = "Rplot%03d.jpg", width = 480, height = 480,
pointsize = 12, quality = 75, bg = "white", res = NA)
png(filename = "Rplot%03d.png", width = 480, height = 480,
pointsize = 12, bg = "white", res = NA)
Arguments
filename |
the name of the output file, up to 511 characters. The page number is substituted if an integer format is included in the character string. (The result must be less than 600 characters long.) |
width |
the width of the device in pixels. |
height |
the height of the device in pixels. |
pointsize |
the default pointsize of plotted text, interpreted at 72 dpi, so one point is approximately one pixel. |
bg |
the initial background colour: can be overridden by setting par("bg"). |
quality |
the ‘quality’ of the JPEG image, as a percentage. Smaller values will give more compression but also more degradation of the image. |
res |
The nominal resolution in dpi which will be recorded in the bitmap file, if a positive integer. |
Details
Plots in PNG and JPEG format can easily be converted to many other bitmap formats, and both can be displayed in most modern web browsers. The PNG format is lossless and is best for line diagrams and blocks of solid colour. The JPEG format is lossy, but may be useful for image plots, for example. The BMP format is standard on Windows, and supported elsewhere.
png supports transparent backgrounds on 16-bit
(‘High Color’) or better screens: use bg = "transparent".
Not all PNG viewers render files with transparency correctly.
Windows imposes limits on the size of bitmaps: these are not
documented in the SDK and may depend on the version of Windows.
It seems width and height are limited to
2^{15}-1 and there is a 16Mb limit on the total amount
of memory in Windows 95/98/Me.
By default no resolution is recorded in the file. Readers will often assume nominal resolution of 72dpi when none is recorded. As resolutions in PNG files are recorded in pixels/metre, the dpi value will be changed slightly.
Value
A plot device is opened: nothing is returned to the R interpreter.
Warning
If you plot more than one page on one of these devices and do not
include something like %d for the sequence number in
file, the file will contain the last page plotted.
Note
These devices effectively plot on a hidden screen and then copy the image to the required format. This means that they have the same colour handling as the actual screen device, and work best if that is set to a 24-bit or 32-bit colour mode.
See Also
Devices, dev.print,
bitmap
Examples
## copy current plot to a (large) PNG file
## Not run: dev.print(png, file="myplot.png", width=1024, height=768)
png(file="myplot.png", bg="transparent")
plot(1:10)
rect(1, 5, 3, 7, col="white")
dev.off()
jpeg(file="myplot.jpeg")
example(rect)
dev.off()
## End(Not run)