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MATLAB

IMVIEW v2

My new MATLAB image display function, imview, has been updated and is ready for wide use.

Steve Eddins

• 6 min read

Back in December, I posted about a new image display function that I was creating. I intend to use this new function, called imview, instead of the venerable imshow.

As of today, I think imview is ready for wide use, if you're interested. You need three File Exchange submissions:

If you have downloaded any of these before today, please update to the latest versions and give them a try. (Also, if you use the Add-On Manager to install the imview add-on, you'll need to manually correct the path to move the add-on folder to the top of the path list. This is because of an ancient, do-nothing stub function in the Image Processing Toolbox that is also called imview. I'm hoping that MathWorks will remove the stub function in a future release.)

Aside: The Image Processing Toolbox development team has also been working on image display improvements lately, although in a somewhat different direction. If you regularly work with very large images in MATLAB, I recommend that you take a look at imageshow.

Motivation for IMVIEW

To briefly recap what I posted before, imshow is a 31-year-old function with default behaviors that were based on computer monitor characteristics in the 1990s and which are no longer appropriate today, especially regarding image interpolation. It also has several behaviors that are inconsistent with the way other high-level graphics behave, particularly with respect to resizing figure windows, setting axes limits, and interacting with other graphics elements plotted into the same axes. The figure-resizing behavior is especially glitchy, having been evolved to deal with several situations that were not envisioned (by me) in the original design, including docked figures, MATLAB Online, and Live Editor embedded figures.

Also, I'm taking advantage of having a fresh new function to add some enhancements that I've long been interested in. The big new thing is showing (and changing) the image zoom level dynamically. I've added an axes toolbar button to toggle the zoom-level display. See the Examples section below for some pictures.

Comparing IMVIEW and IMSHOW

  • The function imview does not resize the figure containing the image display. Instead, the image is displayed in the current axes in the current figure.
  • The function imview displays the image using bilinear interpolation and antialiasing by default, unless individual pixels are larger than about 0.25 inches. In that case, the interpolation switches automatically to nearest neighbor, and a pixel grid is shown. The function imshow uses nearest neighbor interpolation by default.
  • The function imview displays the zoom level (as a percentage) at the lower right of the image. The zoom level can be changed directly by clicking on the zoom level display and editing it. The zoom level is displayed by default, but you can override that using the ShowZoomLevel argument. You can also override it by changing a setting.
  • Unlike imshow, imview does not explicitly set the axes XLim and YLim properties. Instead, it sets the XLimitMethod and YLimitMethod properties to "tight". With this choice, the axes limits will tightly enclose the data contained by the axes, including the image and anything else that might also be plotted in the same axes. Also unlike imshow, the axes limits will continue to automatically adjust to additional data being plotted there.
  • When displaying an indexed image, imview sets the colormap of the axes instead of the figure.
  • The function imview supports AlphaData input.
  • When reading image data from a PNG file, imview will read and use pixel transparency data if it is in the file.
  • The function imview does not have an input argument for controlling the initial zoom level, as InitialMagnification does for imshow. Instead, call setImageZoomLevel or zoomImage after calling imview.
  • The function imview does not observe the MATLAB Image Display Preferences.

Examples

Display Truecolor Image

A = imread("capitol-building-stained-glass.jpg");
whos A

  Name         Size                   Bytes  Class    Attributes

  A         2662x3550x3            28350300  uint8              

imview(A)

figure_0.png

Display Grayscale Image

B = imread("margaret-d-foster.jpg");
whos B

  Name         Size                 Bytes  Class    Attributes

  B         4181x5154            21548874  uint8              

imview(B)

figure_1.png

Display Binary Image

C = imread("US2484408-drawings-page-1-cropped.png");
whos C

  Name         Size                Bytes  Class    Attributes

  C         1086x1801            1955886  uint8              

imview(C)

figure_2.png

Display Indexed Image

[X,map] = imread("trees.tif");
whos X map

  Name        Size             Bytes  Class     Attributes

  X         258x350            90300  uint8               
  map       256x3               6144  double              

imview(X,map)

figure_3.png

Set the Zoom Level Directly Using the Zoom Level Display

imview(X,map)

figure_4.png

Click on the zoom level display at the lower right and then change it to a different zoom level.

image_0.png

Here is the resulting image at 3000% zoom. Notice that individual pixels are automatically outlined using pixelgrid when they get this large.

image_1.png

Use Axes Toolbar Button to Show or Hide Zoom Level

Click on the button with the "%" icon to show or hide the zoom level.

image_2.png

Use Named Argument to Show or Hide Zoom Level

imview(A,ShowZoomLevel = true)

imview(A,ShowZoomLevel = false)

Change the Zoom Level Setting

Whether imview shows or hides the zoom level display by default is controlled by a setting. Use the settings interface to programmatically change this setting. You can make the change temporary, or you can make it persist from one MATLAB session to another.

s = settings;
s.imview

Make a temporary change:

s.imview.ShowZoomLevel.TemporaryValue = false;

Make a persistent change:

s.imview.ShowZoomLevel.PersonalValue = false;

See Pixel Grid Automatically at Extreme Zoom Levels

imview(A)
setImageZoomLevel(6000)

figure_5.png

Set the Gray Limits Manually

The dataset in this example is 1-month rainfall for December 2024, 0.5 degree resolution, IMERG program, downloaded from https://neo.gsfc.nasa.gov/view.php?datasetId=GPM_3IMERGM on 25-Jan-2025. The colormap is the same colormap used on that web page. The data is in millimeters, and the color scale is intended to from 1 to 2000 mm.

load nasa-rainfall-05-degrees-dec-2024 R map
imview(R,GrayLimits=[1 2000])
colormap(map)
axis on
box on
colorbar

figure_6.png

Set the Gray Limits to the Full Data Range

D = magic(25);
imview(D, GrayLimits="datarange", Interpolation="nearest")
colorbar

figure_7.png

Display Image Using a Spatial Reference

This example requires Image Processing Toolbox. The task can also be accomplished without the Image Processing Toolbox by setting the XData and YData properties of the image.

Display an image so that each pixel is 0.001 x 0.001 in the x-y domain. Zoom into the center of the image. Turn the axes display on so that the x and y tick labels are visible.

ref = imref2d(size(C),0.001,0.001);
imview(C, SpatialReference = ref)
setImageZoomLevel(50)
axis on

figure_8.png

Display Image with Visible Axes

imview(C)
axis on
box on

figure_9.png

Display Image and Plot New Data

Unlike imshow, the function imview does not prevent the axes object from automatically readjusting its limits to respond to additional plotted data. The axes does, however, continue to maintain a data aspect ratio of [1 1 1].

imview(C)
hold on
rectangle(Position = [0 0 2000 2000],...
    Curvature = [1 1],...
    EdgeColor = "red",...
    LineWidth = 3);
hold off
axis on
box on

figure_10.png