View Image Sequences in Video Viewer

This section describes how to use the Video Viewer app to view image sequences and provides information about configuring the app.

Open Data in Video Viewer App

This example shows how to view multi-slice volumetric data in Video Viewer.

Load the image sequence into the MATLAB^® workspace. For this example, load the MRI data from the file mristack.mat, which is included in the imdata folder. This creates a variable named mristack in your workspace. The variable is an array of 21 grayscale frames containing MRI images of the brain. Each frame is a 256-by-256 array of uint8 data.

load mristack

mristack       256x256x21       1276256     uint8

Click Video Viewer in the apps gallery and select the Import from workspace option on the File menu. You can also call implay, specifying the name of the image sequence variable as an argument.

implay(mristack)

Video Viewer opens, displaying the first frame of the image sequence. Note how Video Viewer displays information about the image sequence, such as the size of each frame and the total number of frames, at the bottom of the window.

Explore Image Sequence Using Playback Controls

To view the image sequence or video as an animation, click the Play button in the Playback toolbar, select Play from the Playback menu, or press P or the Space bar. By default, Video Viewer plays the image sequence forward, once in its entirety, but you can view the frames in the image sequence in many ways, described in this table. As you view an image sequence, Video Viewer updates the Status Bar at the bottom of the window.

Viewing Option	Playback Control	Keyboard Shortcut
Specify the direction in which to play the image sequence.	Click the Playback mode button in the Playback toolbar or select Playback Modes from the Playback menu. You can select Forward, Backward, or AutoReverse. As you click the playback mode button, Video Viewer cycles through these options and the appearance changes to indicate the current selection. Video Viewer uses plus (+) and minus (-) signs to indicate playback direction in the Current Frame display. When you play a video backwards, the frame numbers displayed are negative. When you are in AutoReverse mode, Video Viewer uses plus signs to indicate the forward direction.	A
View the sequence repeatedly.	Click the Repeat button in the Playback toolbar or select Playback Modes > Repeat from the Playback menu. You toggle this option on or off.	R
Jump to a specific frame in the sequence.	Click the Jump to button in the Playback toolbar or select Jump to from the Playback menu. This option opens a dialog box in which you can specify the number of the frame.	J
Stop the sequence.	Click the Stop button in the Playback toolbar or select Stop from the Playback menu. This button is only enabled when an image sequence is playing.	S
Step through the sequence, one frame at a time, or jump to the beginning or end of the sequence (rewind).	Click one of the navigation buttons in the Playback toolbar, in the desired direction, or select an option, such as Fast Forward or Rewind from the Playback menu.	Arrow keys Page Up/Page Down L (last frame) F (first frame)

Examine Frame More Closely

Video Viewer supports several tools listed in the Tools menu and on the Toolbar that you can use to examine the frames in the image sequence more closely.

Viewing Option	Playback Control
Zoom in or out on the image, and pan to change the view.	Click one of the zoom buttons in the toolbar or select Zoom In or Zoom Out from the Tools menu. Click the Pan button in the toolbar or select Pan from the Tools menu. If you click Maintain fit to window button in the toolbar or select Maintain fit to window or from the Tools menu, the zoom and pan buttons are disabled.
Examine an area of the current frame in detail.	Click the Pixel region button in the Playback toolbar or select Pixel Region from the Tools menu.
Export frame to Image Viewer	Click the Export to Image Tool button in the Playback toolbar or select Export to Image Tool from the File menu. Video Viewer opens an Image Viewer app containing the current frame.

Specify Frame Rate

To decrease or increase the playback rate, select Frame Rate from the Playback menu, or use the keyboard shortcut T. The Frame Rate dialog box displays the frame rate of the source, lets you change the rate at which Video Viewer plays the image sequence or video, and displays the actual playback rate. The playback rate is the number of frames that Video Viewer processes per second.

If you want to increase the actual playback rate, but your system's hardware cannot keep up with the desired rate, select the Allow frame drop to achieve desired playback rate check box. This parameter enables Video Viewer to achieve the playback rate by dropping frames. When you select this option, the Frame Rate dialog box displays several additional options that you can use to specify the minimum and maximum refresh rates. If your hardware allows it, increase the refresh rate to achieve a smoother playback. However, if you specify a small range for the refresh rate, the computed frame replay schedule may lead to a choppy replay, and a warning will appear.

Specify Colormap

To specify the colormap to apply to the intensity values, select Colormap from the Tools menu, or use the keyboard shortcut C. Video Viewer displays a dialog box that enables you to change the colormap.

Use the Colormap parameter to specify a particular colormap.

If you know that the pixel values do not use the entire data type range, you can select the Specify range of displayed pixel values check box and enter the range for your data. The dialog box automatically displays the range based on the data type of the pixel values.

Get Information about an Image Sequence

To view basic information about the image data, click the Video Information button in the toolbar or select Video Information from the Tools menu. Video Viewer displays a dialog box containing basic information about the image sequence, such as the size of each frame, the frame rate, and the total number of frames.

Configure Video Viewer App

The Configuration dialog box enables you to change the appearance and behavior of the player. To open the Configuration dialog box, select File > Configuration > Edit. To load a preexisting configuration set, select File > Configuration > Load.

The Configuration dialog box contains four tabs: Core, Sources, Visuals, and Tools. On each tab, select a category and then click Properties to view configuration settings.

The following table lists the options that are available for each category on every pane.

Pane	Option Category	Option Descriptions
Core	General UI	Display the full path check box — Select to display the full path to the video data source in the title bar. By default, Video Viewer displays a shortened name in the title bar.
Core	Source UI	Keyboard commands respect playback mode check box — Select to make keyboard shortcut keys aware of your playback mode selection. If you clear this check box, the keyboard shortcut keys behave as if the playback mode is set to Forward play and Repeat is set to off. Recently used sources list parameter — Specifies the number of sources listed in the File menu.
Sources	Simulink	Load Simulink model if not open check box — You must have Simulink installed. Connect scope on selection of: — Signal lines only or signal lines and blocks. You must have Simulink installed.
Sources	File	Default open file path parameter — Specify the directory that is displayed in the Connect to File dialog box when you click File > Open.
Sources	Workspace	There are no options associated with this selection.
Visuals	Video	There are no options associated with this selection.
Tools	Image Tool	Open new Image Tool window for each export check box — Opens a new Image Viewer for each exported frame.
Tools	Pixel Region	There are no options associated with this selection.
Tools	Image Navigation Tools	There are no options associated with this selection.
Tools	Instrumentation Sets	There are no options associated with this selection.

Save Image Viewer App Configuration Settings

To save your configuration settings for future use, select File > Configuration Set > Save as.

Note

By default, Video Viewer uses the configuration settings from the file implay.cfg. If you want to store your configuration settings in this file, you should first create a backup copy of the file.