Interlacing Problems

Let's see how the two frames - called from now on fields - are interlaced:

In reality, the second field is positioned directly under the first field. As you can see, the two fields alternate, forming the frame. The first field is the first frame and the second one is the second field is the second frame.

Here's an image that shows this better:

A properly interlaced frame (click to enlarge)

If you look at it, you can bearly see interlacing artifacts. In this case the interlacing is a good thing, it manages to bundle together two frames without noticeable loss. Let's look at the two fields that compose the frame:

The first field in the frame (click to enlarge)

The second field in the frame (click to enlarge)

Problems occur when the camera changes its location or when another scene starts.

This is best illustrated in the image below:

A transition between two scenes is a perfect example (click to enlarge)

The two fields that form the image belong to different scenes:

The first field in the frame (click to enlarge)

The second field in the frame (click to enlarge)

Because each field has it's own different time but they're mixed together into a single frame, it is not possible to deinterlace the frames, maintain 25 frames per second and keep all the information in the images, at least one of these parameters has to be sacrificed.

This is where different deinterlacing algorithms have a lot of work to do and this is where optimizations appear.

This page was viewed by 694 people. It belongs to the Deinterlacing guide, listed in the video category. Print this guide.