MATLAB: How to prevent axes clipping when changing zoom on a tall image

Image Processing ToolboxMATLAB

How do I prevent axes clipping when changing zoom on a tall image?

When I have a tall skinny image, it renders at proper aspect ratio, but when I zoom, the image is restricted to the initial viewport size. How can I allow zoom to preserve aspect ratio without clipping the width of my tall image?

Best Answer

There are two possible solutions to this issue, one using Image Processing Toolbox and one with base MATLAB.

Image Processing Toolbox - Image Viewer app:

The Image Viewer app (which can be opened via the "imtool" function) that comes with the Image Processing Toolbox has the desired zooming behavior. It can be used as follows:

im = imread('TallSkinny.png');  % Plots your image
imtool(im);

When zooming, the width of the tall image will expand to fill the figure. Here is a link to the documentation about "imtool" and the Image Viewer app:

https://www.mathworks.com/help/releases/R2016b/images/ref/imtool.html

Base MATLAB - No Axes Clipping:

In base MATLAB, you can change the Axes properties for "DataAspectRatioMode" and "Clipping" to achieve the desired behavior:

I = imread('TallSkinny.png');
imshow(I)
ax = gca;
ax.DataAspectRatioMode = 'manual';
ax.Clipping = 'off';

This should yield similar zooming behavior as does the "imtool" solution. Here is a link to the documentation about Axes properties:

https://www.mathworks.com/help/releases/R2016b/matlab/ref/axes-properties.html

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MATLAB: Does imshow image shift the other plots and text on the UIAxes in app designer

When 'imshow' is called, it rearranges a few of the axes properties of app.UIAxes. It changes the direction of the y-axis ('YDir'), the modes of both the aspect ratios ('PlotBoxAspectRatioMode' and 'DataAspectRatioMode'), and the values of the aspect ratios ('PlotBoxAspectRatio' and 'DataAspectRatio'). We will need to preserve the original values and reassign them after 'imshow' is called.

The first row of pixels within an image is normally at the top. By default, the 'imshow' function inverts the y-axis direction when the image is displayed on an axes by setting the 'YDir' property to 'reverse.' To revert the y-axis direction after calling 'imshow', set the 'YDir' property to 'normal'. Then, to preserve the orientation of the image, flip the image using 'flip'.

Next, the 'imshow' function sets the 'DataAspectRatioMode' property of app.UIAxes to 'manual' and the 'PlotBoxAspectRatioMode' to 'auto'. The 'DataAspectRatio' property of app.PlotLegend is then rearranged to match the ratio of the image, and the 'PlotBoxAspectRatioMode' modifies itself accordingly.

In the code below, the original 'PlotBoxAspectRatio' is preserved, then the 'PlotBoxAspectRatioMode' is set to 'manual' while the 'DataAspectRatioMode' is set to 'auto'. Finally, the 'PlotBoxAspectRatio' is reassigned to the property's original value and the 'DataAspectRatio' property modifies itself accordingly.

          % Button pushed function: Button
          function ButtonPushed(app, event)
              v = [60,0; 75,0; 75,2; 60,2];
              f = [1, 2, 3, 4, 1];
              sqHandle = patch(app.UIAxes,'vertices', v, 'faces', f, ...
                  'FaceColor', 'k', 'LineStyle', 'none');
              txtHandle = text(app.UIAxes, 80, 0, 'test text','Fontsize',12,'VerticalAlignment', 'bottom');
              hold(app.PlotLegend,'on');
              pbarOriginal = pbaspect(app.UIAxes); % preserve the original PlotBoxAspectRatio
              I = imread('myImage.jpg');
              I = flip(I); % flip the image
              imshow(I,'Parent',app.UIAxes,'XData',[90,95],'YData',[0,2]);
              % Revert the properties back to their original values
              app.UIAxes.YDir = 'normal';
              app.UIAxes.PlotBoxAspectRatioMode = 'manual';
              app.UIAxes.DataAspectRatioMode = 'auto';
              app.UIAxes.PlotBoxAspectRatio = pbarOriginal;
          end

MATLAB: Correlation between ‘FontSize’ for “insertText” function and resulting letter/textbox height in pixels

The "insertText" function uses TrueType fonts to render the text. TrueType is software that is embedded in both Windows and Mac operating systems and is outside of MATLAB. Currently there is no way for "insertText" to request the font height in pixels using the underling rendering library. However, once the font is rendered, the "insertText" function will "know" the font height in pixels but this value is currently inaccessible from outside the function.

As a workaround, you can measure the number of pixels of the output text to get the relationship between font height in pixels and the font size.

The workaround steps are as follows:

1. Select whatever string you wish to render.

2. Set the 'BoxOpacity' parameter of "insertText" to 1 to see the background box.

3. Use "imtool" function to measure the height of the box. "imtool" doc is linked below:

https://www.mathworks.com/help/releases/R2018a/images/ref/imtool.html

Best Answer

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MATLAB: Does imshow image shift the other plots and text on the UIAxes in app designer

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