Video Frames:

    De-Interlacing, Interlacing, Re-interlacing.  What are they?

Each frame of conventional video (e.g. DV video) is made up of two Fields.  How do I know if my movie is interlaced?
These are normally called the odd and even fields.
The odd field is made from the lines (or rasters) of the frame with odd numbers. 1,3,5,7,9,11,13 .. etc
The even field is made from the lines (or rasters) of the frame with even numbers. 2,4,6,8,10,12  .. etc

These two fields are normally taken from different points in time. A normal capture sequence for a video camera will be:
Even Field (frame1)
Odd Field (frame1)
Even Field (frame2)
Odd Field (frame2)
and so on..

The time between each field will be half a frame time e.g. for PAL video at 25 fps this will be 0.02 seconds.
When two fields are put together to make a single frame - this is called Interlacing.
Due to this time difference, if both fields are viewed as a frame (interlaced), and the subject of the frame is moving, then a problem known as "field tearing" will be seen. (See the segment image below)


To get around this, only a single field is usually used if an image is being taken from video, but scaled to twice it's real height. This does not have the field tearing problem but actually has half the vertical detail (pixel resolution). (See the segment image below)


The ImageIP application SupaImage allows you to use both fields to make one high quality frame without field tearing.
De-interlacing is the method of taking two fields of a video frame.
Re-interlacing is the opposite, where the two fields are combined to make single frame.

How do I know if my movie is interlaced?

The easiest way to find out if your video clip is made from interlaced video is to use Quick-Snap
Load the movie clip into Quick-Snap and press the 'Interlaced Fields' toggle button a few times. If your movie is interlaced you will see the extra field of detail dissapear and reappear in the preview window. If nothing happens then it's not interlaced and there will be no need to de-interlace it. If it is interlaced, then turn the 'Interlaced Fields' toggle button ON, and press 'Snap' to save the image. Load the saved image into SupaImage using the "Load 1 & 2 from video frame" option on the File menu, and use SupaImage to enhance it. The result will be a re-interlaced frame but without field tearing.