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</div><div class="twikiRevInfo"><span class="twikiGrayText"><span class="twikiToolbarElem">Cinelerra.DefeatingInterlacing</span><span class="twikiToolbarElem">r1.2 - 21 Dec 2003 - 19:49 - <a class="twikiLink" href="../Main/AlexFerrer">AlexFerrer</a></span><span class="twikiToolbarElem"><a href="#TopicEnd">topic&nbsp;end</a></span></span></div></div>
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<h3><a name="DefeatingInterlacing"> </a> <a class="twikiLink" href="DefeatingInterlacing">DefeatingInterlacing</a> </h3>
<p />
Interlacing is done on most video sources because it costs too much to build progressive scanning cameras and progressive scanning CRT's. Many a consumer has been dissapointed to spend 5 paychecks on a camcorder and discover what horrible jagged images it produces on a computer monitor.
<p />
As for progressive scanning camcorders, forget it. Cost factors are probably going to keep progressive scanning cameras from ever equalling the spatial resolution of interlaced cameras. Interlacing is here to stay. That's why they made deinterlacing effects in Cinelerra.
<p />
We don't believe there has ever been a perfect deinterlacing effect. They're either irreversible or don't work. Cinelerra cuts down the middle by providing deinterlacing tools that are irreversible sometimes and don't work sometimes but are neither one or the other.
<p />
<h4><a name="Line_Doubling"> </a> Line Doubling </h4>
<p />
This one is done by the Deinterlace effect when set to Odd lines or Even lines. When applied to a track it reduces the vertical resolution by 1/2 and gives you progressive frames with stairstepping. This is only useful when followed by a scale effect which reduces the image to half its size.
<p />
<h4><a name="Line_averaging"> </a> Line averaging </h4>
<p />
The Deinterlace effect when set to Average even lines or Average odd lines does exactly what line doubling does except instead of making straight copies of the lines it makes averages of the lines. This is actually useful for all scaling.
<p />
There's an option for adaptive line averaging which selects which lines to line average and which lines to leave interlaced based on the difference between the lines. It doesn't work.
<p />
<h4><a name="Inverse_Telecine"> </a> Inverse Telecine </h4>
<p />
This is the most effective deinterlacing tool when the footage is an NTSC TV broadcast of a film. See <a class="twikiLink" href="VideoInverseTelecine">VideoInverseTelecine</a>.
<p />
<h4><a name="Time_base_correction"> </a> Time base correction </h4>
<p />
The first three tools either destroy footage irreversibly or don't work sometimes. Time base correction is last because it's the perfect deinterlacing tool. It leaves the footage intact. It doesn't reduce resolution, perceptually at least. It doesn't cause jittery timing.
<p />
The <span class="twikiNewLink" style="background : #FFFFCE;"><font color="#0000FF">VideoFramesToFields</font><a href="http://www.ftconsult.com/twiki/bin/edit/Cinelerra/VideoFramesToFields?topicparent=Cinelerra.DefeatingInterlacing"><sup>?</sup></a></span> effect converts each frame to two frames, so it must be used on a timeline whose project frame rate is twice the footage's frame rate. In the first frame it puts a line averaged copy of the even lines. In the second frame it puts a line averaged copy of the odd lines. When played back at full framerates it gives the illusion of progressive video with no loss of detail.
<p />
Best of all, this effect can be reversed with the Fields to frames nonrealtime effect. That one combines two frames of footage back into the one original interlaced frame of half the framerate.
<p />
Unfortunately, the output of <span class="twikiNewLink" style="background : #FFFFCE;"><font color="#0000FF">VideoFramesToFields</font><a href="http://www.ftconsult.com/twiki/bin/edit/Cinelerra/VideoFramesToFields?topicparent=Cinelerra.DefeatingInterlacing"><sup>?</sup></a></span> can't be compressed as efficiently as the original because it introduces vertical twitter and a super high framerate.
<p />
Interlaced 29.97fps footage can be made to look like film by applying <span class="twikiNewLink" style="background : #FFFFCE;"><font color="#0000FF">VideoFramesToFields</font><a href="http://www.ftconsult.com/twiki/bin/edit/Cinelerra/VideoFramesToFields?topicparent=Cinelerra.DefeatingInterlacing"><sup>?</sup></a></span> and then reducing the project frame rate of the resulting 59.94fps footage to 23.97fps. This produces no timing jitter and the occasional odd field gives the illusion of more detail than there would be if you just line averaged the original.
<p />
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-- <a class="twikiLink" href="../Main/AlexFerrer">AlexFerrer</a> - 19 Dec 2003
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