readJPEG

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Read a bitmap image stored in the JPEG format

Reads an image from a JPEG file/content into a raster array.

Keywords
IO
Usage
readJPEG(source, native = FALSE)
Arguments
source
Either name of the file to read from or a raw vector representing the JPEG file content.
native
determines the image representation - if FALSE (the default) then the result is an array, if TRUE then the result is a native raster representation.
Value

If native is 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 native is TRUE then an object of the class nativeRaster is returned instead. The latter cannot be easily computed on but is the most efficient way to draw using rasterImage.Most common files decompress into RGB (3 channels) or Grayscale (1 channel). Note that Grayscale images cannot be directly used in rasterImage unless native is set to TRUE because rasterImage requires RGB or RGBA format (nativeRaster is always 8-bit RGBA).JPEG doesn't support alpha channel, you may want to use PNG instead in such situations.

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. readJPEG will preserve values exactly as they are encoded in the file.

See Also

rasterImage, writeJPEG

Aliases
  • readJPEG
Examples
library(jpeg) # 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) }
Documentation reproduced from package jpeg, version 0.1-8, License: GPL-2 | GPL-3

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