User`s guide

Working with Image Data in MATLAB Workspace

7-15

Clean up — Always remove image acquisition objects from memory, and the

variables that reference them, when you no longer need them.

delete(vid)

clear vid

Determining the Data Type of Image Frames

By default, the toolbox returns image frames in the data type used by the image

acquisition device. If there is no MATLAB data type that matches the object's native

data type, getdata chooses a MATLAB data type that preserves numerical accuracy.

For example, in RGB 555 format, each color component is expressed in 5-bits. getdata

returns each color as a uint8 value.

You can specify the data type you want getdata to use for the returned data. For

example, you can specify that getdata return image frames as an array of class double.

To see a list of all the data types supported, see the getdata reference page.

The following example illustrates the data type of returned image data.

Create an image acquisition object — This example creates a video input object

for a Matrox image acquisition device. To run this example on your system, use the

imaqhwinfo function to get the object constructor for your image acquisition device

and substitute that syntax for the following code.

vid = videoinput('matrox',1);

Bring a single frame into the workspace — Call the getsnapshot function to

bring a frame into the workspace.

frame = getsnapshot(vid);

View the class of the returned data — Use the class function to determine the

data type used for the returned image data.

class(frame)

ans =

uint8

Clean up — Always remove image acquisition objects from memory, and the

variables that reference them, when you no longer need them.

delete(vid)