15
the frame period you have selected, after you press
'Apply
-(Changes)' button. You will be
given a choice between a smaller ROI height and a lower frame rate. Applying your choice
the application will make the smallest possible change.
Figure 7, Changing ROI of the video capture
Any changes you make are not reflected in the camera until the
Apply
-Changes button is
pressed. The
'Apply'
button collects the values of the various settings in the dialog,
verifies them, and updates the camera. If there is an error in your selected settings a
warning will pop-up and the offending value will not be sent to the camera.
The
Preview Window
is exactly 640x480 pixels. Selecting ROI sizes bigger than 640x480
pixels will only show you the
upper left hand part of the image that fits in 640x480 preview
windows
. (In fact the camera only sends the upper 640x480 pixels for that is all the USB
2.0 can support in real time.) The alternative to viewing only part of the ROI is to scale the
image down so it fits in the
Preview Window
. This is done by marking
‘Fit in Window’
check box. In that mode not every pixel in the ROI will be displayed. Downscaling preview
images with regular patterns can potentially create the fringe effect. It will not affect actual
captured images.
FRAME RATE AND EXPOSURE
You can type desired values for the
Frame Rate
and
Exposure
in their respective edit
boxes. The
Frame Rate
(fps) edit box allows the user to set the video capture frame rate
in frames per second. The
Exp
(us) edit box is used to define the exposure in
microseconds. Here is where you can change the exposure if you want it to be less than
the frame period. For obvious reasons, the exposure time can not be longer than the frame
rate. This limit is enforced by the program when you press the
'Apply'
button. You will be
informed about this action and the new exposure value by the information window pop-up.
