User manual

Small Vision System User Manual 46
void svsVideoClose(void)
Closes the connection to the video capture device(s). Usually not needed, since the
connection will be closed when a program exits. However, it's nice to do this, and some
drivers under MS Windows are less forgiving.
5.2.4 Capture Device Format Parameters
These global parameters dictate the basic format for analog framegrabber devices. They should be set
before calling the svsVideoOpen function. The default formats are for the STH-V3 system.
int svsDualCaptureFormat
A global integer that determines the type of video capture system. Values are:
• CAP_INTERLACE Single video stream with alternate lines containing
left and right images.
• CAP_DUAL Dual video stream requiring two capture boards.
• CAP_RGCOMPONENT Dual video stream using a single RGB capture
board. Left image is on the R component, right on
the G component.
This parameter is not relevant for the MEGA-D digital system.
int svsHasFields
A global integer that determines whether the capture board driver can save single fields to
memory. Values are 0 (only interlaced frames) or 1 (can save fields). Not relevant for the
MEGA-D digital system.
int svsVideoFormat
A global integer that determines the pixel format of the video stream captured to memory.
Only used in Video for Windows drivers. The two supported values are:
• BI_YVU9 9 bits/pixel, with reduced color information. This is the typical
format for interlaced and dual capture.
• BI_RGB 24 bits/pixel RGB component. This value is only used for RGB
component capture cards.
int svsVideoBPP
A global integer that determines the number of bits per pixel. Only used with Video for
Windows drivers. Should be set to 9 for BI_YVU9, and 24 for BI_RGB.
5.2.5 Frame Size Parameters
Most framegrabbers support some way to specify the image size, that is, the height and width of the
returned image. The cameras themselves output an analog signal that has a native resolution, for
example, NTSC cameras have a native resolution of 640 x 480. For most analog framegrabbers, the
image size implicitly determines the subsampling of the image, e.g., specifying a 320x240 image size
means the framegrabber subsamples a 640x480 (NTSC) camera image by 2.
Some analog framegrabbers also support subwindowing, where only a portion of the image is actually
digitized and returned. There is no current support in the SVS interface libraries for analog framegrabber
subwindowing, although it would not be difficult to add.
Some cameras, especially digital cameras, support direct control over the number of pixels returned in
each image. For these cameras, explict specification of sampling modes and subwindowing is possible,
and the 1394 OHCI interface library for the MEGA-D supports these modes.