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How are Odd and Even Fields Differentiated in an Interlaced Video Signal?



Primary Software: Driver Software>>NI-IMAQ
Primary Software Version: 3.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
When a camera outputs an interlaced video signal, how are the odd and even fields differentiated so the frame grabber or monitor knows what field is being sent?

Solution:
In the standard for RS-170, the last line of active video is either a full or a half line of data depending on whether a field is odd or even. At the end of an odd field, there is an extra half line of data that is sent indicating the following field is even. Similarly, the last line of the even field is a full line of active video data, indicating the following field will be odd (see image).

National Instruments frame grabbers are able to recognize this characteristic and mark fields as either odd or even.



Related Links:
Developer Zone Tutorial: Anatomy of a Video Signal
Knowledgebase 2I09GHZO: When Acquiring an Image, What Field Is Taken First, Odd or Even?
Knowledgebase 1VL02L7O: What Is the Relationship Between Frame/Field Mode and Interlaced/Non-Interlaced?

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Report Date: 02/15/2002
Last Updated: 07/27/2009
Document ID: 2IE8TDZO

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