Plots Images

1. Plot Images Matplotlib
2. Box Plots Images

image {graphics}

R Documentation

Display a Color Image

Description

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Creates a grid of colored or gray-scale rectangles with colorscorresponding to the values in z. This can be used to displaythree-dimensional or spatial data aka images.This is a generic function.

NOTE: the grid is drawn as a set of rectangles by default;see the useRaster argument to draw the grid as a raster image.

The function hcl.colors provides a broad range of sequentialcolor palettes that are suitable for displaying ordered data, withn giving the number of colors desired.

Usage

Arguments

x, y	locations of grid lines at which the values in z aremeasured. These must be finite, non-missing and in (strictly)ascending order. By default, equallyspaced values from 0 to 1 are used. If x is a list,its components x$x and x$y are used for xand y, respectively. If the list has component z thisis used for z.
z	a numeric or logical matrix containing the values to be plotted(NAs are allowed). Note that x can be used insteadof z for convenience.
zlim	the minimum and maximum z values for which colorsshould be plotted, defaulting to the range of the finite values ofz. Each of the given colors will be used to color anequispaced interval of this range. The midpoints of theintervals cover the range, so that values just outside the rangewill be plotted.
xlim, ylim	ranges for the plotted x and y values,defaulting to the ranges of x and y.
col	a list of colors such as that generated byhcl.colors, gray.colors or similarfunctions.
add	logical; if TRUE, add to current plot (and disregardthe following four arguments). This is rarely useful becauseimage ‘paints’ over existing graphics.
xaxs, yaxs	style of x and y axis. The default 'i' isappropriate for images. See par.
xlab, ylab	each a character string giving the labels for the x andy axis. Default to the ‘call names’ of x or y, or to' if these were unspecified.
breaks	a set of finite numeric breakpoints for the colours:must have one more breakpoint than colour and be in increasingorder. Unsorted vectors will be sorted, with a warning.
oldstyle	logical. If true the midpoints of the colour intervalsare equally spaced, and zlim[1] and zlim[2] were takento be midpoints. The default is to have colour intervals of equallengths between the limits.
useRaster	logical; if TRUE a bitmap raster is used toplot the image instead of polygons. The grid must be regular in thatcase, otherwise an error is raised. For the behaviour when this isnot specified, see ‘Details’.
...	graphical parameters for plot may also bepassed as arguments to this function, as can the plot aspect ratioasp and axes (see plot.window).

Details

The length of x should be equal to the nrow(z)+1 ornrow(z). In the first case x specifies the boundariesbetween the cells: in the second case x specifies the midpointsof the cells. Similar reasoning applies to y. It probablyonly makes sense to specify the midpoints of an equally-spacedgrid. If you specify just one row or column and a length-one xor y, the whole user area in the corresponding direction isfilled. For logarithmic x or y axes the boundaries betweencells must be specified.

Rectangles corresponding to missing values are not plotted (and so aretransparent and (unless add = TRUE) the default backgroundpainted in par('bg') will show through and if that istransparent, the canvas colour will be seen).

If breaks is specified then zlim is unused and thealgorithm used follows cut, so intervals are closed onthe right and open on the left except for the lowest interval which isclosed at both ends.

The axes (where plotted) make use of the classes of xlim andylim (and hence by default the classes of x andy): this will mean that for example dates are labelled assuch.

Notice that image interprets the z matrix as a table off(x[i], y[j]) values, so that the x axis corresponds to rownumber and the y axis to column number, with column 1 at the bottom,i.e. a 90 degree counter-clockwise rotation of the conventionalprinted layout of a matrix.

Images for large z on a regular grid are rendered moreefficiently with useRaster = TRUE and can prevent rareanti-aliasing artifacts, but may not be supported by all graphicsdevices. Some devices (such as postscript and X11(type = 'Xlib')) which do not support semi-transparent colours may emitmissing values as white rather than transparent, and there may belimitations on the size of a raster image. (Problems with therendering of raster images have been reported by users ofwindows() devices under Remote Desktop, at least under itsdefault settings.)

The graphics files in PDF and PostScript can be much smaller underthis option.

If useRaster is not specified, raster images are used when thegetOption('preferRaster') is true, the grid is regularand either dev.capabilities('rasterImage')$rasterImageis 'yes' or it is 'non-missing' and there are no missingvalues.

Note

Originally based on a function by Thomas Lumley.

See Also

filled.contour or heatmap which canlook nicer (but are less modular),contour;The lattice equivalent of image islevelplot.

hcl.colors, gray.colors,hcl, hsv, par.

dev.capabilities to see if useRaster = TRUE issupported on the current device.

Examples

In this article, you’ll learn to save plots in R programming. You’ll learn to save plots as bitmap and vector images.

All the graphs (bar plot, pie chart, histogram, etc.) we plot in R programming are displayed on the screen by default.

We can save these plots as a file on disk with the help of built-in functions.

It is important to know that plots can be saved as bitmap image (raster) which are fixed size or as vector image which are easily resizable.

How to save plot as a bitmap image?

Most of the image we come across like jpeg or png are bitmap image. They have a fixed resolution and are pixelated when zoomed enough.

Functions that help us save plots in this format are jpeg(), png(), bmp() and tiff().

We will use the temperature column of built-in dataset airquality for the remainder of this section as example.

Save as Jpeg image

To save a plot as jpeg image we would perform the following steps.

Please note that we need to call the function dev.off() after all the plotting, to save the file and return control to the screen.

This will save a jpeg image in the current directory. The resolution of the image by default will be 480x480 pixel.

Save as png image

We can specify the resolution we want with arguments width and height.

Plot Images Matplotlib

We can also specify the full path of the file we want to save if we don’t want to save it in the current directory.

The following code saves a png file with resolution 600x350.

Box Plots Images

Save as bmp image

Similarly, we can specify the size of our image in inch, cm or mm with the argument units and specify ppi with res.

The following code saves a bmp file of size 6x4 inch and 100 ppi.

Save as tiff image

Finally, if we want to save in the tiff format, we would only change the first line to tiff(filename = 'saving_plot3')

How to save plot as a vector image?

We can save our plots as vector image in pdf or postscript formats.

The beauty of vector image is that it is easily resizable. Zooming on the image will not compromise its quality.

Save as pdf file

To save a plot as pdf we do the following.

Save as postscript file

Similarly, to save the plot as a postscript file, we change the first line to postscript(file='saving_plot4.ps').

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