|GNU Octave Manual Version 3|
by John W. Eaton, David Bateman, Søren Hauberg
Paperback (6"x9"), 568 pages
RRP £24.95 ($39.95)
30.2 Displaying Images
A natural part of image processing is visualization of an image.
The most basic function for this is the
imshow function that
shows the image given in the first input argument. This function uses
an external program to show the image. If gnuplot 4.2 or later is
available it will be used to display the image, otherwise the
xloadimage program is used. The
actual program can be selected with the
- Function File: imshow (im)
- Function File: imshow (im, limits)
- Function File: imshow (im, map)
- Function File: imshow (rgb, ...)
- Function File: imshow (filename)
- Function File: imshow (..., string_param1, value1, ...)
- Display the image im, where im can be a 2-dimensional
(gray-scale image) or a 3-dimensional (RGB image) matrix.
If limits is a 2-element vector
[low, high], the image is shown using a display range between low and high. If an empty matrix is passed for limits, the display range is computed as the range between the minimal and the maximal value in the image.
If map is a valid color map, the image will be shown as an indexed image using the supplied color map.
If a file name is given instead of an image, the file will be read and shown.
If given, the parameter string_param1 has value value1. string_param1 can be any of the following:
- value1 is the display range as described above.
See also image, imagesc, colormap, gray2ind, rgb2ind
- Function File: image (img)
- Function File: image (x, y, img)
- Display a matrix as a color image. The elements of x are indices
into the current colormap, and the colormap will be scaled so that the
extremes of x are mapped to the extremes of the colormap.
It first tries to use
xv, and then
xloadimage. The actual program used can be changed using the
The axis values corresponding to the matrix elements are specified in x and y. If you're not using gnuplot 4.2 or later, these variables are ignored.
See also imshow, imagesc, colormap, image_viewer
- Function File: imagesc (a)
- Function File: imagesc (x, y, a)
- Function File: imagesc (..., limits)
- Function File: imagesc (h, ...)
- Function File: h = imagesc (...)
- Display a scaled version of the matrix a as a color image. The
colormap is scaled so that the entries of the matrix occupy the entire
colormap. If limits = [lo, hi] are given, then that
range is set to the 'clim' of the current axes.
The axis values corresponding to the matrix elements are specified in x and y, either as pairs giving the minimum and maximum values for the respective axes, or as values for each row and column of the matrix a.
See also image, imshow, clim, caxis
- Function File: [fcn, default_zoom] = image_viewer (fcn, default_zoom)
- Change the program or function used for viewing images and return the
imshowfunction is called it will launch an external program to display the image. The default behaviour is to use gnuplot if the installed version supports image viewing, and otherwise try the programs
xloadimage. Using this function it is possible to change that behaviour.
When called with one input argument images will be displayed by saving the image to a file and the system command command will be called to view the image. The command must be a string containing
%swill be replaced by the filename of the image, and the
%fwill (if present) be replaced by the zoom factor given to the
imagefunction. For example,
image_viewer ("eog %s");
changes the image viewer to the
With two input arguments, images will be displayed by calling the function function_handle. For example,
image_viewer (data, @my_image_viewer);
sets the image viewer function to
my_image_viewer. The image viewer function is called with
my_image_viewer (x, y, im, zoom, data)
where x and y are the axis of the image, im is the image variable, and data is extra user-supplied data to be passed to the viewer function.
With three input arguments it is possible to change the zooming. Some programs (like
xloadimage) require the zoom factor to be between 0 and 100, and not 0 and 1 like Octave assumes. This is solved by setting the third argument to 100.
See also image, imshow
|ISBN 095461206X||GNU Octave Manual Version 3||See the print edition|