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Singlef - Single Field Grab and Display

Win32 Systems (Win95, 98, Me, NT, 2000 and XP)

This program which was derived from our PXCDRAW2 sample with just a few simple modifications shows how to grab a single field of video and display it in a window.

Standard interlaced video is comprised of two fields that are interlaced to make a full frame of video. In the case of NTSC video, the size of a frame is 640 x 480. Hence, the size of the individual fields is 640 x 240. The horizontal dimension is unchanged, but there are only half as many lines in a field as in a frame. When we display a field of video we crop the horizontal dimension from 640 to 320 to keep the aspect ratio the same as it was at 640 x 480 and make the images look correct.

This sample creates a window just large enough to display a single field of video and illustrates the correct coding for grabbing just a single field from the PXC200A.

The important changes between this program and PXCDRAW2 can be seen by looking at the AppInit() function to see how we handle the variables ImageMaxX and ImageMaxY. These two variables control both the image and window sizes.

Another important change between this program and PXCDRAW2 is the Grab() function. In this program we OR together several flags. Two of them are SINGLE_FLD and FIELD0. We only grab field 0. You can modifiy the Grab() command to grab field 1, but you should probably avoid grabbing EITHER field at random because the image will bounce up and down within the window.