Désentrelacement

The désentrelacement is the process which makes it possible to post in progressive Balayage an image transmitted in mode interlaced.

In interlaced mode, a half of image is transmitted to each screen: odd lines for the first image, line pairs for the second and so on. The signal is thus composed of odd and even screens following one another. In progressive posting, a screen corresponds to a whole image, an even line succeeds an odd line in the screen.

If an interlaced video signal is posted such as it is by a monitor with progressive sweeping, then each screen is regarded an image and not as a half image. One can thus have with the screen of the lines belonging to two successive images and not with the same image, which creates Artifact S.

Désentrelacé posting comprises some advantages compared to interlaced:

the perceived vertical resolution of an interlaced image is equivalent to 60 % of the number of lines posted with the screen: indeed, the frequency being weaker, one with above the other a well lit point and a point having lost intensity, from where a less good perception of the details; the side resolution is not it not affectée
for example, the perception of a posting of high-resolution 1080i (: 1920×: 1080, interlaced) are equivalent to a posting in weaker theory 720p (: 1280×: 720, progressive) in spite of a more significant number of lines;
not of flickering of brought closer horizontal reasons, not of artefact at the time of the Dolly S rapids;
video equipment of simpler treatment;
easier compression.

Methods of désentrelacement

There exist several methods of désentrelacement, each one presenting its clean Artifact S.

; Weaving (waving)

This method simply consists in adding an odd screen to an even screen and to post both unit. The even and odd lines correspond to the same image only once on two.

This method produces “teeth of saw”, effects of “Venetian blind”, and in addition, one divides by two the rate of image; it has the same defect as posting without treatment, but with less flutter thus a better vertical resolution.

; Désentrelacement inter-screen (blending)

That consists in calculating the missing lines starting from the screens the preceding one and following.

This method produces a “ghostly” effect, the image “is softened” vertically.

; Désentrelacement intra-screen (line doubling)

That consists in increasing each screen to adapt it to the definition of the screen, which amounts considering that one has a signal with lower resolution.

This method degrades the vertical resolution.

; Recombining of the image

That consists in giving together the screens of the same half-image, an image is then posted twice continuation (as it at the time of a cinematographic Projection is besides the case).

This method respects the initial image and has a better stability, but requires “to disentangle the screens”. It is called sometimes “telecinema reverses”, but it is a technique different from the Kinescopage.

; Another method

Tutorial explaining how désentrelacer under after effects: : http://www.creativecow.net/articles/kramer_andrew/deinterlace/deinterlace.html

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