Preview of live video data
himage = preview(...)
preview(obj) creates a Video Preview window
that displays live video data for video input object
obj. The window also
displays the timestamp and video resolution of each frame, the current frame rate, and the
current status of
obj. The Video Preview window displays the video data
at 100% magnification. The size of the preview image is determined by the value of the video
Components of a Video Preview Window
The Video Preview window remains active until it is either stopped using
stoppreview or closed using
closepreview. If you
delete the object, by calling
delete(obj), the Video Preview window stops
previewing and closes automatically.
preview(obj,himage) displays live video data
for video input object
obj in the image object specified by the handle
preview scales the image data to fill the
entire area of the image object but does not modify the values of any image object
properties. Use this syntax to preview video data in a custom GUI of your own design (see
himage = preview(...) returns
himage, a handle to the image object containing the previewed data. To
obtain a handle to the figure window containing the image object, use the
ancestor function. For more information about using image objects, see
image. See the Custom Update Function section for more information
about the image object returned.
The behavior of the Video Preview window depends on the video input object's current state and trigger configuration.
Preview Window Behavior
Displays a live view of the image being acquired from the device, for all
trigger types. The image is updated to reflect changes made to configurations of
object properties. (The
Video Preview window might drop some data frames, but this will not affect the frames logged to memory or disk.
The Image Acquisition Toolbox Preview window supports the display of up to 16-bit
image data. The Preview window was designed to only show 8-bit data, but many cameras
return 10-, 12-, 14-, or 16-bit data. The Preview window display supports these higher
bit-depth cameras. However, larger bit data is scaled to 8-bit for the purpose of
displaying previewed data. To capture the image data in the Preview window in its full bit
depth for grayscale images, set the
PreviewFullBitDepth property to
Custom Update Function
preview creates application-defined data for the image object,
himage, assigning it the name
'UpdatePreviewWindowFcn' and setting its value to an empty array
). You can configure the value of the
'UpdatePreviewWindowFcn' application data and retrieve its value using
getappdata functions, respectively.
'UpdatePreviewWindowFcn' will not necessarily be called for every
frame that is acquired. If a new frame is acquired and the
'UpdatePreviewWindowFcn' for the previous frame has not yet finished
executing, no update will be generated for the new frame. If you need to execute a function
for every acquired frame, use the
You can use this function to define custom processing of the previewed image data. When
preview invokes the function handle you specify, it passes three
arguments to your function:
obj— The video input object being previewed
event— An event structure containing image frame information. For more information, see below.
himage— A handle to the image object that is being updated
The event structure contains the following fields:
Current image frame specified as an H-by-W-by-B matrix where H and W
are the image height and width, respectively, as specified in the
Character vector specifying current image width and height, as defined
Character vector describing the current acquisition status of the video input object.
Character vector specifying the timestamp associated with the current image frame.
Character vector specifying the current frame rate of the video input object in frames per second.
Create a customized GUI.
figure('Name', 'My Custom Preview Window'); uicontrol('String', 'Close', 'Callback', 'close(gcf)');
Create an image object for previewing.
vidRes = obj.VideoResolution; nBands = obj.NumberOfBands; hImage = image( zeros(vidRes(2), vidRes(1), nBands) ); preview(obj, hImage);
For more information on customized GUIs, see Previewing Data in Custom GUIs.
Introduced before R2006a