User`s guide

7 Working with Acquired Image Data
7-12
• Determines the data type used for the data
• Determines the color space of the data
This section also describes several ways to view acquired image data.
Determining the Dimensions of Image Data
The video format used by the image acquisition device is the primary determinant of the
width, height, and the number of bands in each image frame. Image acquisition devices
typically support multiple video formats. You select the video format when you create the
video input object (described in “Specifying the Video Format” on page 5-11). The video
input object stores the video format in the VideoFormat property.
Industry-standard video formats, such as RS170 or PAL, include specifications of
the image frame width and height, referred to as the image resolution. For example,
the RS170 standard defines the width and height of the image frame as 640-by-480
pixels. Other devices, such as digital cameras, support the definition of many different,
nonstandard image resolutions. The video input object stores the video resolution in the
VideoResolution property.
Each image frame is three dimensional; however, the video format determines the
number of bands in the third dimension. For color video formats, such as RGB, each
image frame has three bands: one each for the red, green, and blue data. Other video
formats, such as the grayscale RS170 standard, have only a single band. The video input
object stores the size of the third dimension in the NumberOfBands property.
Note Because devices typically express video resolution as width-by-height, the toolbox
uses this convention for the VideoResolution property. However, when data is brought
into the MATLAB workspace, the image frame dimensions are listed in reverse order,
height-by-width, because MATLAB expresses matrix dimensions as row-by-column.
ROIs and Image Dimensions
When you specify a region-of-interest (ROI) in the image being captured, the
dimensions of the ROI determine the dimensions of the image frames returned. The
VideoResolution property specifies the dimensions of the image data being provided
by the device; the ROIPosition property specifies the dimensions of the image frames
being logged. See the ROIPosition property reference page for more information.