imager (version 0.31)

plot.cimg: Display an image using base graphics

Description

If you want to control precisely how numerical values are turned into colours for plotting, you need to specify a colour scale using the colourscale argument (see examples). Otherwise the default is "gray" for grayscale images, "rgb" for colour. These expect values in [0..1], so the default is to rescale the data to [0..1]. If you wish to over-ride that behaviour, set rescale=FALSE. See examples for an explanation. If the image is one dimensional (i.e., a simple row or column image), then pixel values will be plotted as a line.

Usage

"plot"(x, frame, xlim = c(1, width(x)), ylim = c(height(x), 1), xlab = "x", ylab = "y", rescale = TRUE, colourscale = NULL, colorscale = NULL, interpolate = TRUE, ...)

Arguments

x

the image

frame

which frame to display, if the image has depth > 1

xlim

x plot limits (default: 1 to width)

ylim

y plot limits (default: 1 to height)

xlab

x axis label

ylab

y axis label

rescale

rescale pixel values so that their range is [0,1]

colourscale, colorscale

an optional colour scale (default is gray or rgb)

interpolate

should the image be plotted with antialiasing (default TRUE)

...

other parameters to be passed to plot.default (eg "main")

See Also

display, which is much faster, as.raster, which converts images to R raster objects

Examples

plot(boats,main="Boats") #extra arguments are passed to default plot function
plot(boats,axes=FALSE,xlab="",ylab="")

#Pixel values are rescaled to 0-1 by default, so that the following two plots are identical
plot(boats)
plot(boats/2,main="Rescaled")
#If you don't want that behaviour, you can set rescale to FALSE, but
#then you need to make sure values are in [0,1]
try(plot(boats,rescale=FALSE)) #Error!
try(plot(boats/255,rescale=FALSE)) #Works
#You can specify a colour scale if you don't want the default one.
#A colour scale is a function that takes pixels values and return an RGB code,
#like R's rgb function,e.g.
rgb(0,1,0)
#Let's switch colour channels
cscale <- function(r,g,b) rgb(b,g,r)
plot(boats/255,rescale=FALSE,colourscale=cscale)
#Display slice of HSV colour space
im <- imfill(255,255,val=1)
im <- list(Xc(im)/255,Yc(im)/255,im) %>% imappend("c")
plot(im,colourscale=hsv,rescale=FALSE,
     xlab="Hue",ylab="Saturation")
#In grayscale images, the colourscale function should take in a single value
#and return an RGB code
boats.gs <- grayscale(boats)
#We use an interpolation function from package scales
cscale <- scales::gradient_n_pal(c("red","purple","lightblue"),c(0,.5,1))
plot(boats.gs,rescale=FALSE,colourscale=cscale)
#Plot a one-dimensional image
imsub(boats,x==1) %>% plot(main="Image values along first column")
#Plotting with and without anti-aliasing:
boats.small <- imresize(boats,.3)
plot(boats.small,interp=TRUE)
plot(boats.small,interp=FALSE)