wavethresh (version 2.2-6)

plot.imwd: Plot Method for an `imwd' object

Description

Images Wavelet Coefficients of a imwd class object

Usage

## S3 method for class 'imwd':
plot(imwd, scaling="by.level", co.type="abs",
     plot.type="mallat", arrangement=c(3,3),
     plot = exists("image", mode="function"),
     transform = FALSE, tfunction = sqrt,
     col = heat.colors(32), ...)

Arguments

imwd

object of class "imwd" containing a wavelet decomposition of an image.

scaling

character string, determining the scaling applied to each sub-image. The values can be "by.level" which means each image is scaled independently to the whole dynamic range of the image, otherwise the whole image is scaled as a whole (as i

co.type

character string, specifying a transform to be applied to the coefficients before display. If co.type=="abs", then the absolute values of the coefficients will be displayed, if co.type=="mabs", then the negative of the a

plot

logical; if TRUE, image is used to display the result.

plot.type

If plot.type=="mallat", then the image within image type of plot as exemplified within Mallat (1989) will be produced. If plot.type=="rows", then the individual level/orientation plots are produced in an array according to the arrangement argu

arrangement

Determines the parameter to pass to mfrow to set up the display for multiple plots per page. The default, c(3,3) specifies 3 rows and 3 columns.

transform

logical; if TRUE, then the function given by argument tfunction is applied.

tfunction

a (vectorizing) function; a transform to apply to the coefficients if transform is true.

col

vector of colors to use for image.

Value

• The matrix of wavelet coefficients packed in Mallat form, returned invisible if plot is true.

Side Effects

An image of the wavelet coefficients is produced if plot is true.

Details

If plot.type=="mallat" then the picture produced is the same as the one described by Mallat 1989. After a decomposition there will be exactly the same number of coefficients as there were pixels in the original image. This function is a good way of plotting all the coefficients, but it means that you can't really see some of the lower resolution images very clearly.

If plot.type=="rows", then each sub-image of the decomposition is plotted at the same size so you can see the lower resolution images. By default the arrangement of each of the sub-images is on a 3x3 array, so three levels can fit onto one plot. If you are using a screen device then it may be desirable to turn on the "ask before you plot" option with dev.ask(), since the coefficients plot may run to a few pages with the "rows" plot.type.

It is not always easy to see exactly what's going on, so there are a few arguments that try to manipulate the (sub)image(s). The scaling argument only works when the plot.type=="mallat" is in force. If scaling is by.level then each subimage is scaled independently, if not then the whole image is scaled at once. The co.type works for both plot types and causes absolute values, negative absolute values or just the coefficients to be plotted - this is useful for enhancing various effects. The most flexible transformation is provided when transform==TRUE, then the function tfunction is applied to all the coefficients and can produce some useful contrast enhancing effects.

At each stage of the decomposition we decompose an image into four images, each of which are half the size of the original (see "imwd" for what these are). Three of the images correspond to wavelet coefficients in the horizontal, vertical and diagonal directions and these form the bottom-right, top-left and top-right sections of the displayed image. The fourth image is further decomposed into another four subimages. Three of which get put into the bottom-right, top-left, and top-right sections OF THE BOTTOM-LEFT part of the previous image and so on and so on. It is impossible to explain this properly in a simple fashion, so the only way to really understand what is going on is to do it yourself and see what happens.

This function is a method for the generic function plot() for class imwd. It can be invoked by calling plot(x) for an object x of the appropriate class, or directly by calling plot.imwd(x) regardless of the class of the object.

See Also

imwd, for references and background.

Examples

example(imwd)
# See the wavelet coefficient in Mallat's form
c.gray <- gray(127:0 / 128)
plot(imwdL, col = c.gray)
plot(imwdL, col = c.gray, scaling = "none")
plot(imwdL, col = c.gray, scaling = "none", co.type = "none")
plot(imwdL, col = c.gray, plot.type = "cols")