Interlacing: How to prevent jagged lines in video
Learn what interlacing is, shows what it looks like, and read suggestions about how to prevent it when creating and editing movies.
Q. What is interlaced video and what is a progressive scan monitor?
A. Most consumer video cameras capture two fields per frame. The two fields are interlaced with each other. That is, the odd horizontal lines are from one field and the even lines are from the other. Televisions display one field after the other, while progressive scan monitors display both fields simultaneously. Computer monitors fall into the progressive scan category.
Example of interlacing
Q. In iDVD and DVD Studio Pro, jagged lines in the video are visible during preview and even after burning to disc in Apple DVD Player. What is this?
A. This may be the effect of displaying interlaced video on a progressive scan monitor.
Q. Why do jagged lines appear?
A. Since the computer monitor doesn't interpret fields like a TV does, you may see interlacing when there is fast camera or object movement. This is the effect of displaying two moments in time simultaneously. When watching the DVD on a normal TV, the interlacing effect is not noticeable.
Q. Is there any way to prevent this?
A. Yes. Some application programs such as Final Cut Pro have an option to de-interlace the video. De-interlacing the video before importing into iDVD or DVD Studio Pro prevents this effect on computer monitors (see Figure 2), though the motion may not be as smooth on a TV. Check the user's manual for your software to see if it offers this feature and how to use it. Also, some video cameras have an option for progressive scan (Canon calls it "Movie Mode"). Shooting video in this way captures an entire frame at a time instead of two fields and prevents the interlacing effect.
Image after correction
DVD Player 4.5 or later (in Mac OS X 10.4 or later) includes an option to deinterlace video. Choose Window > Video Color. In the Video Color window, select the Deinterlace video checkbox.
Q. Why does this effect only occur on DVD-R discs, but not commercial DVD-Video discs?
A. Movies on commercial DVD-Video discs are typically made with film cameras. Unlike video, film does not use fields or interlacing so you do not see this effect.
For more information on fields and interlacing, please see article 58634: "Final Cut Pro: Field Dominance Discussion"