Inter-frame filtering for the deinterlacing tasks

So far, we have discussed purely spatial filtering methods for image and video frame deinterlacing. The spatial approach however does not take into account the temporal continuity of video frames that led to the idea of interlacing to begin with. A different approach that takes into account the differences and similarities between consecutive frames so that missing lines are filled, is called inter-frame filtering. Methods based on this approach rely on blending rows from consecutive frames to construct the deinterlaced version of a frame. In this section, we will discuss two alternative inter-frame methods.

Temporal deinterlacing by field merging

The first inter-frame method used for deinterlacing is field merging. This method is pretty simple and relies on substitution of the missing odd rows of a frame with the odd rows of the next one and consequent substitution of the even rows of the next frame with the even rows of its previous one.

This way, we fill the blank rows and acquire an image with no gaps, but there is a downside; having replaced the rows of an image with rows from a later or earlier frame, we have obviously messed with the temporal consistency within the frame. In simple words, we have included image information that has not happened yet (when using rows from the next frame), or has happened in the past (when using rows from a previous frame). This method is perfectly acceptable when no (or very little) motion exists in the video we are trying to deinterlace, but in scenes with high motion it introduces a new artifact, called a ghosting effect.

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