read.gif & write.gif | R Documentation |
Read and write files in GIF format. Files can contain single images or multiple frames. Multi-frame images are saved as animated GIF's.
read.gif(filename, frame=0, flip=FALSE, verbose=FALSE)
write.gif(image, filename, col="gray", scale=c("smart", "never", "always"),
transparent=NULL, comment=NULL, delay=0, flip=FALSE, interlace=FALSE)
filename |
Character string with name of the file. In case of
|
image |
Data to be saved as GIF file. Can be a 2D matrix or 3D array. Allowed formats in order of preference:
|
frame |
Request specific frame from multiframe (i.e., animated) GIF file.
By default all frames are read from the file ( |
col |
Color palette definition. Several formats are allowed:
Usually palette will consist of 256 colors, which is the maximum allowed by GIF format. By default, grayscale will be used. |
scale |
There are three approaches to rescaling the data to required [0, 255] integer range:
|
delay |
In case of 3D arrays the data will be stored as animated GIF, and
|
comment |
Comments in text format are allowed in GIF files. Few file viewers can access them. |
flip |
By default data is stored in the same orientation as data
displayed by |
transparent |
Optional color number to be shown as transparent. Has to be an
integer in [0:255] range. NA's in the |
interlace |
GIF files allow image rows to be |
verbose |
Display details sections encountered while reading GIF file. |
Palettes often contain continuous colors, such that swapping palettes or
rescaling of the image date does not affect image apperance in a drastic way.
However, when working with non-continuous color-maps one should always provide
image in [0:255] integer range (and set scale="never"
), in order to
prevent scaling.
If NA
or other infinite numbers are found in the image
by
write.gif
, they will be converted to numbers given by transparent
.
If transparent
color is not provided than it will be created, possibly
after reshretching.
There are some GIF files not fully supported by read.gif
function:
"Plain Text Extension" is not supported, and will be ignored.
Multi-frame files with unique settings for each frame have to be read frame by frame. Possible settings include: frames with different sizes, frames using local color maps and frames using individual transparency colors.
Function write.gif
does not return anything.
Function read.gif
returns a list with following fields:
image |
matrix or 3D array of integers in [0:255] range. |
col |
color palette definitions with number of colors ranging from 1
to 256. In case when |
comment |
Comments imbedded in GIF File |
transparent |
color number corresponding to transparent color. If none
was stated than NULL, otherwise an integer in [0:255] range. In order for
|
Jarek Tuszynski (SAIC) jaroslaw.w.tuszynski@saic.com. Encoding Algorithm adapted from code by Christoph Hohmann, which was adapted from code by Michael Mayer. Parts of decoding algorithm adapted from code by David Koblas.
Ziv, J., Lempel, A. (1977) An Universal Algorithm for Sequential Data Compression, IEEE Transactions on Information Theory, May 1977.
Displaying of images can be done through functions:
graphics:image
(part of R),
fields::image.plot
and fields::add.image
or
spatstat:plot.im
, and possibly many other functions.
Displayed image can be saved in GIF, JPEG or PNG format using several
different functions, like R2HTML:HTMLplot
.
Functions for directly reading and writing image files:
read.pnm
and pixmap::write.pnm
can
process PBM, PGM and PPM images (file types supported by ImageMagic software)
read.ENVI
and write.ENVI
from this package
can process files in ENVI format. ENVI files can store 2D images and 3D data
(multi-frame images), and are supported by most GIS (Geographic Information
System) software including free "freelook".
There are many functions for creating and managing color palettes:
fields::tim.colors
contains a palette similar to Matlab's
jet palette (see examples for simpler implementation)
gplots::rich.colors
contains two palettes of continuous colors.
Functions RColorBrewer::brewer.pal
and
epitools::colorbrewer.palette
contain tools for generating palettes.
grDevices::rgb
and grDevices::hsv
create palette from RGB or HSV 3-vectors.
grDevices::col2rgb
translates
palette colors to RGB 3-vectors.
# visual comparison between image and plot
write.gif( volcano, "volcano.gif", col=terrain.colors, flip=TRUE,
scale="always", comment="Maunga Whau Volcano")
y = read.gif("volcano.gif", verbose=TRUE, flip=TRUE)
image(y$image, col=y$col, main=y$comment, asp=1)
# browseURL("file://volcano.gif") # inspect GIF file on your hard disk
# test reading & writing
col = heat.colors(256) # choose colormap
trn = 222 # set transparent color
com = "Hello World" # imbed comment in the file
write.gif( volcano, "volcano.gif", col=col, transparent=trn, comment=com)
y = read.gif("volcano.gif")
# This tested col==y$col, but colours may or may not have an alpha channel
# and for col this changed in R 4.0
stopifnot(volcano==y$image, trn==y$transparent, com==y$comment)
# browseURL("file://volcano.gif") # inspect GIF file on your hard disk
# create simple animated GIF (using image function in a loop is very rough,
# but only way I know of displaying 'animation" in R)
x <- y <- seq(-4*pi, 4*pi, len=200)
r <- sqrt(outer(x^2, y^2, "+"))
image = array(0, c(200, 200, 10))
for(i in 1:10) image[,,i] = cos(r-(2*pi*i/10))/(r^.25)
write.gif(image, "wave.gif", col="rainbow")
y = read.gif("wave.gif")
for(i in 1:10) image(y$image[,,i], col=y$col, breaks=(0:256)-0.5, asp=1)
# browseURL("file://wave.gif") # inspect GIF file on your hard disk
# Another neat animation of Mandelbrot Set
jet.colors = colorRampPalette(c("#00007F", "blue", "#007FFF", "cyan", "#7FFF7F",
"yellow", "#FF7F00", "red", "#7F0000")) # define "jet" palette
m = 400
C = complex( real=rep(seq(-1.8,0.6, length.out=m), each=m ),
imag=rep(seq(-1.2,1.2, length.out=m), m ) )
C = matrix(C,m,m)
Z = 0
X = array(0, c(m,m,20))
for (k in 1:20) {
Z = Z^2+C
X[,,k] = exp(-abs(Z))
}
image(X[,,k], col=jet.colors(256))
write.gif(X, "Mandelbrot.gif", col=jet.colors, delay=100)
# browseURL("file://Mandelbrot.gif") # inspect GIF file on your hard disk
file.remove("wave.gif", "volcano.gif", "Mandelbrot.gif")
# Display interesting images from the web
## Not run:
url = "http://www.ngdc.noaa.gov/seg/cdroms/ged_iib/datasets/b12/gifs/eccnv.gif"
y = read.gif(url, verbose=TRUE, flip=TRUE)
image(y$image, col=y$col, breaks=(0:length(y$col))-0.5, asp=1,
main="January Potential Evapotranspiration mm/mo")
url = "http://www.ngdc.noaa.gov/seg/cdroms/ged_iib/datasets/b01/gifs/fvvcode.gif"
y = read.gif(url, flip=TRUE)
y$col[y$transparent+1] = NA # mark transparent color in R way
image(y$image, col=y$col[1:87], breaks=(0:87)-0.5, asp=1,
main="Vegetation Types")
url = "http://talc.geo.umn.edu/people/grads/hasba002/erosion_vids/run2/r2_dems_5fps(8color).gif"
y = read.gif(url, verbose=TRUE, flip=TRUE)
for(i in 2:dim(y$image)[3])
image(y$image[,,i], col=y$col, breaks=(0:length(y$col))-0.5,
asp=1, main="Erosion in Drainage Basins")
## End(Not run)
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