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\name{readJPEG}
\alias{readJPEG}
\title{
Read a bitmap image stored in the JPEG format
}
\description{
Reads an image from a JPEG file/content into a raster array.
}
\usage{
readJPEG(source, native = FALSE)
}
\arguments{
\item{source}{Either name of the file to read from or a raw vector
representing the JPEG file content.}
\item{native}{determines the image representation - if \code{FALSE}
(the default) then the result is an array, if \code{TRUE} then the
result is a native raster representation.}
}
%\details{
%}
\value{
If \code{native} is \code{FALSE} then an array of the dimensions height
x width x channels. If there is only one channel the result is a
matrix. The values are reals between 0 and 1. If \code{native} is
\code{TRUE} then an object of the class \code{nativeRaster} is
returned instead. The latter cannot be easily computed on but is the
most efficient way to draw using \code{rasterImage}.
Most common files decompress into RGB (3 channels) or
Grayscale (1 channel). Note that Grayscale images
cannot be directly used in \code{\link{rasterImage}} unless
\code{native} is set to \code{TRUE} because \code{rasterImage} requires
RGB or RGBA format (\code{nativeRaster} is always 8-bit RGBA).
JPEG doesn't support alpha channel, you may want to use PNG instead in
such situations.
}
%\references{
%}
%\author{
%}
\note{
CMYK JPEG images saved by Adobe Photoshop may have inverted ink values due
to a bug in Photoshop. Unfortunately this includes some sample CMYK
images that are floating around, so beware of the source when
converting the result to other color spaces. \code{readJPEG} will
preserve values exactly as they are encoded in the file.
}
\seealso{
\code{\link{rasterImage}}, \code{\link{writeJPEG}}
}
\examples{
# read a sample file (R logo)
img <- readJPEG(system.file("img", "Rlogo.jpg", package="jpeg"))
# read it also in native format
img.n <- readJPEG(system.file("img", "Rlogo.jpg", package="jpeg"), TRUE)
# if your R supports it, we'll plot it
if (exists("rasterImage")) { # can plot only in R 2.11.0 and higher
plot(1:2, type='n')
rasterImage(img, 1.2, 1.27, 1.8, 1.73)
rasterImage(img.n, 1.5, 1.5, 1.9, 1.8)
}
}
\keyword{IO}
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