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Setting Driver Properties
62 ViewCast
The reference width and height represent the full uncropped size of the incoming video. Your crop
settings are interpreted relative to this reference size. For example, if you are capturing 525-line video,
with a reference size of 640 x 480, and your crop rectangle is (0, 0, 640, 480), then your video is
effectively uncropped. But if you are capturing 625-line video, with a reference size of 768 x 576, the
same (0, 0, 640, 480) crop specification truncate the right and bottom edges of the video.
Granularity
Most video data capture formats impose restrictions on the possible width and/or height of the video,
referred to as granularity restrictions. For example, the I420 capture format requires that the capture
width be a multiple of 4 and the capture height be a multiple of 2.
The granularities for the various color formats are as follows:
Format
Horizontal
Vertical
RGB32
4
1
RGB24
4
1
RGB555
4
1
Greyscale
4
1
YUY2
4
1
UYVY
4
1
I420
4
2
YVU9
4
4
[none]
4
1
[any]
4
4
The Granularity controls show the granularity restrictions for the selected video format, and assist you in
choosing crop and output sizes that observe those restrictions.
Figure 58. Capture drop-down list
Because you can set the preview and capture pins to different color formats, they can have different
granularities. When you open the Size and Crop tab, the Capture and Preview fields are initialized to the
current or most recently used format for the selected pin (Figure 58).